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 $82.35   13.792%   $93.7077   $93.71   $93.70   $93.70  
  Purchase #2 $208.79   13.467%   $236.9077   $236.91   $236.90   $236.90  
  Purchase #3 $157.76   4.390%   $164.6857   $164.69   $164.70   $164.70  
  Purchase #4 $113.49   4.527%   $118.6277   $118.63   $118.65   $118.60  
  Purchase #5 $125.77   13.195%   $142.3654   $142.37   $142.35   $142.40  
  Purchase #6 $110.47   7.506%   $118.7619   $118.76   $118.75   $118.80  
  Purchase #7 $136.78   8.429%   $148.3092   $148.31   $148.30   $148.30  
  7 purchase totals = $935.41       $1,023.3653   $1,023.38   $1,023.35   $1,023.40