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 $86.67   8.755%   $94.258   $94.26   $94.25   $94.30  
  Purchase #2 $13.63   5.783%   $14.4182   $14.42   $14.40   $14.40  
  Purchase #3 $119.94   13.253%   $135.8356   $135.84   $135.85   $135.80  
  Purchase #4 $69.56   10.649%   $76.9674   $76.97   $76.95   $77.00  
  Purchase #5 $105.68   11.430%   $117.7592   $117.76   $117.75   $117.80  
  Purchase #6 $218.73   11.858%   $244.667   $244.67   $244.65   $244.70  
  Purchase #7 $69.73   5.229%   $73.3762   $73.38   $73.40   $73.40  
  7 purchase totals = $683.94       $757.2816   $757.30   $757.25   $757.40