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 $46.32   5.163%   $48.7115   $48.71   $48.70   $48.70  
  Purchase #2 $32.32   8.475%   $35.0591   $35.06   $35.05   $35.10  
  Purchase #3 $197.51   9.142%   $215.5664   $215.57   $215.55   $215.60  
  Purchase #4 $12.35   12.237%   $13.8613   $13.86   $13.85   $13.90  
  Purchase #5 $13.97   6.848%   $14.9267   $14.93   $14.95   $14.90  
  Purchase #6 $214.29   9.412%   $234.459   $234.46   $234.45   $234.50  
  Purchase #7 $56.63   6.538%   $60.3325   $60.33   $60.35   $60.30  
  7 purchase totals = $573.39       $622.9165   $622.92   $622.90   $623.00