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 $61.51   7.742%   $66.2721   $66.27   $66.25   $66.30  
  Purchase #2 $118.86   12.438%   $133.6438   $133.64   $133.65   $133.60  
  Purchase #3 $105.94   5.744%   $112.0252   $112.03   $112.05   $112.00  
  Purchase #4 $140.85   11.602%   $157.1914   $157.19   $157.20   $157.20  
  Purchase #5 $131.91   4.663%   $138.061   $138.06   $138.05   $138.10  
  Purchase #6 $116.99   7.649%   $125.9386   $125.94   $125.95   $125.90  
  Purchase #7 $125.25   3.470%   $129.5962   $129.60   $129.60   $129.60  
  7 purchase totals = $801.31       $862.7283   $862.73   $862.75   $862.70