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 $107.37   11.533%   $119.753   $119.75   $119.75   $119.80  
  Purchase #2 $180.96   4.374%   $188.8752   $188.88   $188.90   $188.90  
  Purchase #3 $159.44   7.240%   $170.9835   $170.98   $171.00   $171.00  
  Purchase #4 $43.41   11.453%   $48.3817   $48.38   $48.40   $48.40  
  Purchase #5 $102.51   11.316%   $114.11   $114.11   $114.10   $114.10  
  Purchase #6 $109.75   8.499%   $119.0777   $119.08   $119.10   $119.10  
  Purchase #7 $82.70   12.519%   $93.0532   $93.05   $93.05   $93.10  
  7 purchase totals = $786.14       $854.2343   $854.23   $854.30   $854.40