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 $108.67   12.828%   $122.6102   $122.61   $122.60   $122.60  
  Purchase #2 $229.56   4.807%   $240.5949   $240.59   $240.60   $240.60  
  Purchase #3 $10.64   3.730%   $11.0369   $11.04   $11.05   $11.00  
  Purchase #4 $94.94   11.186%   $105.56   $105.56   $105.55   $105.60  
  Purchase #5 $127.86   7.722%   $137.7333   $137.73   $137.75   $137.70  
  Purchase #6 $22.35   5.796%   $23.6454   $23.65   $23.65   $23.60  
  Purchase #7 $229.41   6.525%   $244.379   $244.38   $244.40   $244.40  
  7 purchase totals = $823.43       $885.5597   $885.56   $885.60   $885.50