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 $209.67   12.747%   $236.3966   $236.40   $236.40   $236.40  
  Purchase #2 $46.95   10.645%   $51.9478   $51.95   $51.95   $51.90  
  Purchase #3 $17.99   11.179%   $20.0011   $20.00   $20.00   $20.00  
  Purchase #4 $132.31   11.642%   $147.7135   $147.71   $147.70   $147.70  
  Purchase #5 $243.97   11.365%   $271.6972   $271.70   $271.70   $271.70  
  Purchase #6 $238.40   3.196%   $246.0193   $246.02   $246.00   $246.00  
  Purchase #7 $21.40   11.461%   $23.8527   $23.85   $23.85   $23.90  
  7 purchase totals = $910.69       $997.6282   $997.63   $997.60   $997.60