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 $202.70   10.259%   $223.495   $223.50   $223.50   $223.50  
  Purchase #2 $75.29   4.217%   $78.465   $78.47   $78.45   $78.50  
  Purchase #3 $11.48   7.760%   $12.3708   $12.37   $12.35   $12.40  
  Purchase #4 $61.25   5.170%   $64.4166   $64.42   $64.40   $64.40  
  Purchase #5 $58.66   3.485%   $60.7043   $60.70   $60.70   $60.70  
  Purchase #6 $213.95   11.758%   $239.1062   $239.11   $239.10   $239.10  
  Purchase #7 $211.64   6.365%   $225.1109   $225.11   $225.10   $225.10  
  7 purchase totals = $834.97       $903.6688   $903.68   $903.60   $903.70