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 $26.39   3.466%   $27.3047   $27.30   $27.30   $27.30  
  Purchase #2 $112.54   11.581%   $125.5733   $125.57   $125.55   $125.60  
  Purchase #3 $78.50   7.543%   $84.4213   $84.42   $84.40   $84.40  
  Purchase #4 $32.76   10.380%   $36.1605   $36.16   $36.15   $36.20  
  Purchase #5 $167.38   5.382%   $176.3884   $176.39   $176.40   $176.40  
  Purchase #6 $89.88   6.729%   $95.928   $95.93   $95.95   $95.90  
  Purchase #7 $187.40   12.458%   $210.7463   $210.75   $210.75   $210.70  
  7 purchase totals = $694.85       $756.5225   $756.52   $756.50   $756.50