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 $56.40   6.335%   $59.9729   $59.97   $59.95   $60.00  
  Purchase #2 $212.53   11.675%   $237.3429   $237.34   $237.35   $237.30  
  Purchase #3 $23.72   5.804%   $25.0967   $25.10   $25.10   $25.10  
  Purchase #4 $21.51   4.152%   $22.4031   $22.40   $22.40   $22.40  
  Purchase #5 $63.77   8.799%   $69.3811   $69.38   $69.40   $69.40  
  Purchase #6 $47.77   4.451%   $49.8962   $49.90   $49.90   $49.90  
  Purchase #7 $28.73   7.302%   $30.8279   $30.83   $30.85   $30.80  
  7 purchase totals = $454.43       $494.9208   $494.92   $494.95   $494.90