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 $151.83   11.508%   $169.3026   $169.30   $169.30   $169.30  
  Purchase #2 $13.69   10.115%   $15.0747   $15.07   $15.05   $15.10  
  Purchase #3 $129.41   8.795%   $140.7916   $140.79   $140.80   $140.80  
  Purchase #4 $112.37   10.821%   $124.5296   $124.53   $124.55   $124.50  
  Purchase #5 $190.82   7.162%   $204.4865   $204.49   $204.50   $204.50  
  Purchase #6 $232.65   7.763%   $250.7106   $250.71   $250.70   $250.70  
  Purchase #7 $115.32   3.338%   $119.1694   $119.17   $119.15   $119.20  
  7 purchase totals = $946.09       $1,024.0650   $1,024.06   $1,024.05   $1,024.10