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 $58.83   7.573%   $63.2852   $63.29   $63.30   $63.30  
  Purchase #2 $34.44   10.217%   $37.9587   $37.96   $37.95   $38.00  
  Purchase #3 $143.61   7.182%   $153.9241   $153.92   $153.90   $153.90  
  Purchase #4 $134.29   5.145%   $141.1992   $141.20   $141.20   $141.20  
  Purchase #5 $59.78   13.520%   $67.8623   $67.86   $67.85   $67.90  
  Purchase #6 $215.75   10.407%   $238.2031   $238.20   $238.20   $238.20  
  Purchase #7 $139.46   10.871%   $154.6207   $154.62   $154.60   $154.60  
  7 purchase totals = $786.16       $857.0533   $857.05   $857.00   $857.10