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 $189.44   6.239%   $201.2592   $201.26   $201.25   $201.30  
  Purchase #2 $50.34   3.102%   $51.9015   $51.90   $51.90   $51.90  
  Purchase #3 $236.73   8.535%   $256.9349   $256.93   $256.95   $256.90  
  Purchase #4 $132.55   4.675%   $138.7467   $138.75   $138.75   $138.70  
  Purchase #5 $52.93   4.212%   $55.1594   $55.16   $55.15   $55.20  
  Purchase #6 $249.38   10.750%   $276.1884   $276.19   $276.20   $276.20  
  Purchase #7 $80.86   4.176%   $84.2367   $84.24   $84.25   $84.20  
  7 purchase totals = $992.23       $1,064.4268   $1,064.43   $1,064.45   $1,064.40