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 $193.62   13.240%   $219.2553   $219.26   $219.25   $219.30  
  Purchase #2 $124.77   5.188%   $131.2431   $131.24   $131.25   $131.20  
  Purchase #3 $206.75   13.471%   $234.6013   $234.60   $234.60   $234.60  
  Purchase #4 $46.61   5.762%   $49.2957   $49.30   $49.30   $49.30  
  Purchase #5 $177.60   13.742%   $202.0058   $202.01   $202.00   $202.00  
  Purchase #6 $203.42   6.339%   $216.3148   $216.31   $216.30   $216.30  
  Purchase #7 $59.87   4.863%   $62.7815   $62.78   $62.80   $62.80  
  7 purchase totals = $1,012.64       $1,115.4975   $1,115.50   $1,115.50   $1,115.50