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 $213.33   13.601%   $242.345   $242.35   $242.35   $242.30  
  Purchase #2 $52.43   6.679%   $55.9318   $55.93   $55.95   $55.90  
  Purchase #3 $17.39   13.821%   $19.7935   $19.79   $19.80   $19.80  
  Purchase #4 $101.37   3.584%   $105.0031   $105.00   $105.00   $105.00  
  Purchase #5 $158.71   9.342%   $173.5367   $173.54   $173.55   $173.50  
  Purchase #6 $197.67   6.614%   $210.7439   $210.74   $210.75   $210.70  
  Purchase #7 $214.41   6.168%   $227.6348   $227.63   $227.65   $227.60  
  7 purchase totals = $955.31       $1,034.9888   $1,034.98   $1,035.05   $1,034.80