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 $64.82   13.331%   $73.4612   $73.46   $73.45   $73.50  
  Purchase #2 $188.34   3.257%   $194.4742   $194.47   $194.45   $194.50  
  Purchase #3 $153.82   9.679%   $168.7082   $168.71   $168.70   $168.70  
  Purchase #4 $36.68   11.582%   $40.9283   $40.93   $40.95   $40.90  
  Purchase #5 $26.29   10.707%   $29.1049   $29.10   $29.10   $29.10  
  Purchase #6 $163.39   13.611%   $185.629   $185.63   $185.65   $185.60  
  Purchase #7 $114.89   13.177%   $130.0291   $130.03   $130.05   $130.00  
  7 purchase totals = $748.23       $822.3349   $822.33   $822.35   $822.30