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 $124.60   10.660%   $137.8824   $137.88   $137.90   $137.90  
  Purchase #2 $19.31   3.179%   $19.9239   $19.92   $19.90   $19.90  
  Purchase #3 $162.26   5.289%   $170.8419   $170.84   $170.85   $170.80  
  Purchase #4 $51.28   9.711%   $56.2598   $56.26   $56.25   $56.30  
  Purchase #5 $198.62   5.316%   $209.1786   $209.18   $209.20   $209.20  
  Purchase #6 $101.57   11.722%   $113.476   $113.48   $113.50   $113.50  
  Purchase #7 $111.63   6.822%   $119.2454   $119.25   $119.25   $119.20  
  7 purchase totals = $769.27       $826.8080   $826.81   $826.85   $826.80