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 $68.93   6.317%   $73.2843   $73.28   $73.30   $73.30  
  Purchase #2 $81.64   13.575%   $92.7226   $92.72   $92.70   $92.70  
  Purchase #3 $216.83   11.548%   $241.8695   $241.87   $241.85   $241.90  
  Purchase #4 $43.42   8.601%   $47.1546   $47.15   $47.15   $47.20  
  Purchase #5 $122.83   4.168%   $127.9496   $127.95   $127.95   $127.90  
  Purchase #6 $151.88   11.740%   $169.7107   $169.71   $169.70   $169.70  
  Purchase #7 $164.61   5.616%   $173.8545   $173.85   $173.85   $173.90  
  7 purchase totals = $850.14       $926.5458   $926.53   $926.50   $926.60