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 $24.77   7.267%   $26.57   $26.57   $26.55   $26.60  
  Purchase #2 $236.29   7.243%   $253.4045   $253.40   $253.40   $253.40  
  Purchase #3 $240.52   8.454%   $260.8536   $260.85   $260.85   $260.90  
  Purchase #4 $73.38   7.502%   $78.885   $78.89   $78.90   $78.90  
  Purchase #5 $119.90   11.138%   $133.2545   $133.25   $133.25   $133.30  
  Purchase #6 $79.33   12.859%   $89.531   $89.53   $89.55   $89.50  
  Purchase #7 $58.47   10.692%   $64.7216   $64.72   $64.70   $64.70  
  7 purchase totals = $832.66       $907.2202   $907.21   $907.20   $907.30