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 $86.74   6.105%   $92.0355   $92.04   $92.05   $92.00  
  Purchase #2 $230.93   8.181%   $249.8224   $249.82   $249.80   $249.80  
  Purchase #3 $208.54   8.222%   $225.6862   $225.69   $225.70   $225.70  
  Purchase #4 $199.50   13.832%   $227.0948   $227.09   $227.10   $227.10  
  Purchase #5 $138.73   10.711%   $153.5894   $153.59   $153.60   $153.60  
  Purchase #6 $30.32   3.676%   $31.4346   $31.43   $31.45   $31.40  
  Purchase #7 $240.87   5.313%   $253.6674   $253.67   $253.65   $253.70  
  7 purchase totals = $1,135.63       $1,233.3303   $1,233.33   $1,233.35   $1,233.30