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 $83.64   11.367%   $93.1474   $93.15   $93.15   $93.10  
  Purchase #2 $141.73   12.158%   $158.9615   $158.96   $158.95   $159.00  
  Purchase #3 $104.30   13.808%   $118.7017   $118.70   $118.70   $118.70  
  Purchase #4 $38.53   9.619%   $42.2362   $42.24   $42.25   $42.20  
  Purchase #5 $112.98   9.618%   $123.8464   $123.85   $123.85   $123.80  
  Purchase #6 $66.63   3.750%   $69.1286   $69.13   $69.15   $69.10  
  Purchase #7 $250.45   4.532%   $261.8004   $261.80   $261.80   $261.80  
  7 purchase totals = $798.26       $867.8222   $867.83   $867.85   $867.70