Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.74   10.714%   $202.3188   $202.32   $202.30   $202.30  
  Purchase #2 $130.41   13.234%   $147.6685   $147.67   $147.65   $147.70  
  Purchase #3 $220.73   5.513%   $232.8988   $232.90   $232.90   $232.90  
  Purchase #4 $151.48   5.796%   $160.2598   $160.26   $160.25   $160.30  
  Purchase #5 $140.32   8.104%   $151.6915   $151.69   $151.70   $151.70  
  Purchase #6 $200.79   12.521%   $225.9309   $225.93   $225.95   $225.90  
  Purchase #7 $240.54   7.398%   $258.3351   $258.34   $258.35   $258.30  
  7 purchase totals = $1,267.01       $1,379.1034   $1,379.11   $1,379.10   $1,379.10