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 $111.90   12.177%   $125.5261   $125.53   $125.55   $125.50  
  Purchase #2 $240.47   8.859%   $261.7732   $261.77   $261.75   $261.80  
  Purchase #3 $39.91   4.604%   $41.7475   $41.75   $41.75   $41.70  
  Purchase #4 $101.95   3.518%   $105.5366   $105.54   $105.55   $105.50  
  Purchase #5 $159.43   12.689%   $179.6601   $179.66   $179.65   $179.70  
  Purchase #6 $178.68   11.127%   $198.5617   $198.56   $198.55   $198.60  
  Purchase #7 $157.72   11.427%   $175.7427   $175.74   $175.75   $175.70  
  7 purchase totals = $990.06       $1,088.5479   $1,088.55   $1,088.55   $1,088.50