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 $116.93   7.107%   $125.2402   $125.24   $125.25   $125.20  
  Purchase #2 $199.46   6.641%   $212.7061   $212.71   $212.70   $212.70  
  Purchase #3 $234.62   5.265%   $246.9727   $246.97   $246.95   $247.00  
  Purchase #4 $6.63   11.142%   $7.3687   $7.37   $7.35   $7.40  
  Purchase #5 $236.44   9.669%   $259.3014   $259.30   $259.30   $259.30  
  Purchase #6 $39.57   6.254%   $42.0447   $42.04   $42.05   $42.00  
  Purchase #7 $92.78   9.579%   $101.6674   $101.67   $101.65   $101.70  
  7 purchase totals = $926.43       $995.3012   $995.30   $995.25   $995.30