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 $87.57   11.513%   $97.6519   $97.65   $97.65   $97.70  
  Purchase #2 $76.90   5.271%   $80.9534   $80.95   $80.95   $81.00  
  Purchase #3 $209.29   11.694%   $233.7644   $233.76   $233.75   $233.80  
  Purchase #4 $154.42   3.389%   $159.6533   $159.65   $159.65   $159.70  
  Purchase #5 $72.38   5.284%   $76.2046   $76.20   $76.20   $76.20  
  Purchase #6 $127.80   3.579%   $132.374   $132.37   $132.35   $132.40  
  Purchase #7 $239.89   8.566%   $260.439   $260.44   $260.45   $260.40  
  7 purchase totals = $968.25       $1,041.0406   $1,041.02   $1,041.00   $1,041.20