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 $214.96   13.847%   $244.7255   $244.73   $244.75   $244.70  
  Purchase #2 $192.39   7.191%   $206.2248   $206.22   $206.20   $206.20  
  Purchase #3 $118.41   12.635%   $133.3711   $133.37   $133.35   $133.40  
  Purchase #4 $40.33   4.863%   $42.2912   $42.29   $42.30   $42.30  
  Purchase #5 $147.90   3.679%   $153.3412   $153.34   $153.35   $153.30  
  Purchase #6 $69.75   9.267%   $76.2137   $76.21   $76.20   $76.20  
  Purchase #7 $53.95   8.677%   $58.6312   $58.63   $58.65   $58.60  
  7 purchase totals = $837.69       $914.7987   $914.79   $914.80   $914.70