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 $54.77   13.164%   $61.9799   $61.98   $62.00   $62.00  
  Purchase #2 $138.38   10.141%   $152.4131   $152.41   $152.40   $152.40  
  Purchase #3 $26.44   12.460%   $29.7344   $29.73   $29.75   $29.70  
  Purchase #4 $198.90   12.720%   $224.2001   $224.20   $224.20   $224.20  
  Purchase #5 $232.80   3.495%   $240.9364   $240.94   $240.95   $240.90  
  Purchase #6 $135.69   12.754%   $152.9959   $153.00   $153.00   $153.00  
  Purchase #7 $42.93   11.580%   $47.9013   $47.90   $47.90   $47.90  
  7 purchase totals = $829.91       $910.1611   $910.16   $910.20   $910.10