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 $29.59   12.164%   $33.1893   $33.19   $33.20   $33.20  
  Purchase #2 $247.70   5.467%   $261.2418   $261.24   $261.25   $261.20  
  Purchase #3 $48.32   4.172%   $50.3359   $50.34   $50.35   $50.30  
  Purchase #4 $80.42   8.548%   $87.2943   $87.29   $87.30   $87.30  
  Purchase #5 $64.88   9.193%   $70.8444   $70.84   $70.85   $70.80  
  Purchase #6 $102.31   10.468%   $113.0198   $113.02   $113.00   $113.00  
  Purchase #7 $166.92   9.552%   $182.8642   $182.86   $182.85   $182.90  
  7 purchase totals = $740.14       $798.7897   $798.78   $798.80   $798.70