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 $91.68   7.301%   $98.3736   $98.37   $98.35   $98.40  
  Purchase #2 $112.78   3.191%   $116.3788   $116.38   $116.40   $116.40  
  Purchase #3 $196.33   12.800%   $221.4602   $221.46   $221.45   $221.50  
  Purchase #4 $94.79   5.844%   $100.3295   $100.33   $100.35   $100.30  
  Purchase #5 $93.91   10.697%   $103.9556   $103.96   $103.95   $104.00  
  Purchase #6 $248.47   5.220%   $261.4401   $261.44   $261.45   $261.40  
  Purchase #7 $111.70   9.438%   $122.2422   $122.24   $122.25   $122.20  
  7 purchase totals = $949.66       $1,024.1800   $1,024.18   $1,024.20   $1,024.20