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 $60.39   12.703%   $68.0613   $68.06   $68.05   $68.10  
  Purchase #2 $178.99   3.653%   $185.5285   $185.53   $185.55   $185.50  
  Purchase #3 $245.97   5.380%   $259.2032   $259.20   $259.20   $259.20  
  Purchase #4 $91.53   5.123%   $96.2191   $96.22   $96.20   $96.20  
  Purchase #5 $59.57   7.420%   $63.9901   $63.99   $64.00   $64.00  
  Purchase #6 $97.94   4.475%   $102.3228   $102.32   $102.30   $102.30  
  Purchase #7 $84.65   3.152%   $87.3182   $87.32   $87.30   $87.30  
  7 purchase totals = $819.04       $862.6432   $862.64   $862.60   $862.60