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 $57.95   10.733%   $64.1698   $64.17   $64.15   $64.20  
  Purchase #2 $16.27   8.144%   $17.595   $17.60   $17.60   $17.60  
  Purchase #3 $208.66   3.703%   $216.3867   $216.39   $216.40   $216.40  
  Purchase #4 $107.89   7.754%   $116.2558   $116.26   $116.25   $116.30  
  Purchase #5 $211.69   3.258%   $218.5869   $218.59   $218.60   $218.60  
  Purchase #6 $118.87   5.252%   $125.1131   $125.11   $125.10   $125.10  
  Purchase #7 $165.59   6.616%   $176.5454   $176.55   $176.55   $176.50  
  7 purchase totals = $886.92       $934.6527   $934.67   $934.65   $934.70