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 $117.67   12.320%   $132.1669   $132.17   $132.15   $132.20  
  Purchase #2 $121.43   6.480%   $129.2987   $129.30   $129.30   $129.30  
  Purchase #3 $34.48   12.817%   $38.8993   $38.90   $38.90   $38.90  
  Purchase #4 $208.92   7.231%   $224.027   $224.03   $224.05   $224.00  
  Purchase #5 $73.88   3.133%   $76.1947   $76.19   $76.20   $76.20  
  Purchase #6 $237.75   11.676%   $265.5097   $265.51   $265.50   $265.50  
  Purchase #7 $144.38   11.680%   $161.2436   $161.24   $161.25   $161.20  
  7 purchase totals = $938.51       $1,027.3399   $1,027.34   $1,027.35   $1,027.30