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 $246.74   8.795%   $268.4408   $268.44   $268.45   $268.40  
  Purchase #2 $175.46   11.331%   $195.3414   $195.34   $195.35   $195.30  
  Purchase #3 $81.71   13.720%   $92.9206   $92.92   $92.90   $92.90  
  Purchase #4 $66.34   13.630%   $75.3821   $75.38   $75.40   $75.40  
  Purchase #5 $107.49   11.447%   $119.7944   $119.79   $119.80   $119.80  
  Purchase #6 $201.91   3.248%   $208.468   $208.47   $208.45   $208.50  
  Purchase #7 $75.78   11.696%   $84.6432   $84.64   $84.65   $84.60  
  7 purchase totals = $955.43       $1,044.9905   $1,044.98   $1,045.00   $1,044.90