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 $94.93   3.716%   $98.4576   $98.46   $98.45   $98.50  
  Purchase #2 $212.62   12.468%   $239.1295   $239.13   $239.15   $239.10  
  Purchase #3 $227.83   5.547%   $240.4677   $240.47   $240.45   $240.50  
  Purchase #4 $43.27   10.298%   $47.7259   $47.73   $47.75   $47.70  
  Purchase #5 $229.34   13.141%   $259.4776   $259.48   $259.50   $259.50  
  Purchase #6 $122.72   7.725%   $132.2001   $132.20   $132.20   $132.20  
  Purchase #7 $89.49   4.228%   $93.2736   $93.27   $93.25   $93.30  
  7 purchase totals = $1,020.20       $1,110.7320   $1,110.74   $1,110.75   $1,110.80