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 $121.71   3.224%   $125.6339   $125.63   $125.65   $125.60  
  Purchase #2 $198.47   3.392%   $205.2021   $205.20   $205.20   $205.20  
  Purchase #3 $112.33   6.317%   $119.4259   $119.43   $119.45   $119.40  
  Purchase #4 $64.56   8.346%   $69.9482   $69.95   $69.95   $69.90  
  Purchase #5 $78.31   10.535%   $86.56   $86.56   $86.55   $86.60  
  Purchase #6 $78.30   13.401%   $88.793   $88.79   $88.80   $88.80  
  Purchase #7 $16.83   11.183%   $18.7121   $18.71   $18.70   $18.70  
  7 purchase totals = $670.51       $714.2752   $714.27   $714.30   $714.20