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 $111.62   12.858%   $125.9721   $125.97   $125.95   $126.00  
  Purchase #2 $45.65   10.357%   $50.378   $50.38   $50.40   $50.40  
  Purchase #3 $179.75   6.393%   $191.2414   $191.24   $191.25   $191.20  
  Purchase #4 $224.93   7.541%   $241.892   $241.89   $241.90   $241.90  
  Purchase #5 $7.68   8.315%   $8.3186   $8.32   $8.30   $8.30  
  Purchase #6 $36.57   6.309%   $38.8772   $38.88   $38.90   $38.90  
  Purchase #7 $101.43   4.271%   $105.7621   $105.76   $105.75   $105.80  
  7 purchase totals = $707.63       $762.4414   $762.44   $762.45   $762.50