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 $97.63   9.386%   $106.7936   $106.79   $106.80   $106.80  
  Purchase #2 $51.38   13.716%   $58.4273   $58.43   $58.45   $58.40  
  Purchase #3 $201.94   12.437%   $227.0553   $227.06   $227.05   $227.10  
  Purchase #4 $72.76   7.420%   $78.1588   $78.16   $78.15   $78.20  
  Purchase #5 $222.61   12.503%   $250.4429   $250.44   $250.45   $250.40  
  Purchase #6 $208.94   3.389%   $216.021   $216.02   $216.00   $216.00  
  Purchase #7 $130.75   4.238%   $136.2912   $136.29   $136.30   $136.30  
  7 purchase totals = $986.01       $1,073.1901   $1,073.19   $1,073.20   $1,073.20