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 $84.61   9.176%   $92.3738   $92.37   $92.35   $92.40  
  Purchase #2 $203.82   9.335%   $222.8466   $222.85   $222.85   $222.80  
  Purchase #3 $87.96   8.543%   $95.4744   $95.47   $95.45   $95.50  
  Purchase #4 $24.33   7.733%   $26.2114   $26.21   $26.20   $26.20  
  Purchase #5 $176.26   10.739%   $195.1886   $195.19   $195.20   $195.20  
  Purchase #6 $5.85   10.159%   $6.4443   $6.44   $6.45   $6.40  
  Purchase #7 $234.53   11.404%   $261.2758   $261.28   $261.30   $261.30  
  7 purchase totals = $817.36       $899.8149   $899.81   $899.80   $899.80