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 $62.81   12.213%   $70.481   $70.48   $70.50   $70.50  
  Purchase #2 $14.65   4.733%   $15.3434   $15.34   $15.35   $15.30  
  Purchase #3 $236.35   7.826%   $254.8468   $254.85   $254.85   $254.80  
  Purchase #4 $157.91   11.590%   $176.2118   $176.21   $176.20   $176.20  
  Purchase #5 $45.82   13.268%   $51.8994   $51.90   $51.90   $51.90  
  Purchase #6 $96.28   10.617%   $106.502   $106.50   $106.50   $106.50  
  Purchase #7 $215.31   12.519%   $242.2647   $242.26   $242.25   $242.30  
  7 purchase totals = $829.13       $917.5491   $917.54   $917.55   $917.50