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 $48.71   3.362%   $50.3476   $50.35   $50.35   $50.30  
  Purchase #2 $231.33   13.126%   $261.6944   $261.69   $261.70   $261.70  
  Purchase #3 $85.28   7.196%   $91.4167   $91.42   $91.40   $91.40  
  Purchase #4 $185.50   6.570%   $197.6874   $197.69   $197.70   $197.70  
  Purchase #5 $39.85   3.460%   $41.2288   $41.23   $41.25   $41.20  
  Purchase #6 $81.80   10.462%   $90.3579   $90.36   $90.35   $90.40  
  Purchase #7 $148.57   7.575%   $159.8242   $159.82   $159.80   $159.80  
  7 purchase totals = $821.04       $892.5570   $892.56   $892.55   $892.50