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 $88.87   5.497%   $93.7552   $93.76   $93.75   $93.80  
  Purchase #2 $248.67   5.602%   $262.6005   $262.60   $262.60   $262.60  
  Purchase #3 $135.71   3.137%   $139.9672   $139.97   $139.95   $140.00  
  Purchase #4 $91.26   10.642%   $100.9719   $100.97   $100.95   $101.00  
  Purchase #5 $141.66   11.681%   $158.2073   $158.21   $158.20   $158.20  
  Purchase #6 $80.27   8.346%   $86.9693   $86.97   $86.95   $87.00  
  Purchase #7 $28.37   3.150%   $29.2637   $29.26   $29.25   $29.30  
  7 purchase totals = $814.81       $871.7351   $871.74   $871.65   $871.90