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 $72.44   4.244%   $75.5144   $75.51   $75.50   $75.50  
  Purchase #2 $91.70   7.203%   $98.3052   $98.31   $98.30   $98.30  
  Purchase #3 $206.42   8.834%   $224.6551   $224.66   $224.65   $224.70  
  Purchase #4 $89.46   3.543%   $92.6296   $92.63   $92.65   $92.60  
  Purchase #5 $112.41   12.491%   $126.4511   $126.45   $126.45   $126.50  
  Purchase #6 $134.58   10.390%   $148.5629   $148.56   $148.55   $148.60  
  Purchase #7 $189.46   7.794%   $204.2265   $204.23   $204.25   $204.20  
  7 purchase totals = $896.47       $970.3448   $970.35   $970.35   $970.40