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 $130.80   7.287%   $140.3314   $140.33   $140.35   $140.30  
  Purchase #2 $225.49   5.571%   $238.052   $238.05   $238.05   $238.10  
  Purchase #3 $141.39   12.376%   $158.8884   $158.89   $158.90   $158.90  
  Purchase #4 $188.93   11.263%   $210.2092   $210.21   $210.20   $210.20  
  Purchase #5 $213.71   7.856%   $230.4991   $230.50   $230.50   $230.50  
  Purchase #6 $178.73   4.866%   $187.427   $187.43   $187.45   $187.40  
  Purchase #7 $133.76   10.810%   $148.2195   $148.22   $148.20   $148.20  
  7 purchase totals = $1,212.81       $1,313.6266   $1,313.63   $1,313.65   $1,313.60