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 $227.97   8.630%   $247.6438   $247.64   $247.65   $247.60  
  Purchase #2 $162.97   6.321%   $173.2713   $173.27   $173.25   $173.30  
  Purchase #3 $51.42   7.139%   $55.0909   $55.09   $55.10   $55.10  
  Purchase #4 $24.50   6.706%   $26.143   $26.14   $26.15   $26.10  
  Purchase #5 $51.88   6.554%   $55.2802   $55.28   $55.30   $55.30  
  Purchase #6 $208.65   4.428%   $217.889   $217.89   $217.90   $217.90  
  Purchase #7 $108.88   4.148%   $113.3963   $113.40   $113.40   $113.40  
  7 purchase totals = $836.27       $888.7145   $888.71   $888.75   $888.70