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 $239.66   7.783%   $258.3127   $258.31   $258.30   $258.30  
  Purchase #2 $103.76   9.746%   $113.8724   $113.87   $113.85   $113.90  
  Purchase #3 $119.45   5.328%   $125.8143   $125.81   $125.80   $125.80  
  Purchase #4 $157.82   7.397%   $169.4939   $169.49   $169.50   $169.50  
  Purchase #5 $245.70   12.233%   $275.7565   $275.76   $275.75   $275.80  
  Purchase #6 $141.97   4.568%   $148.4552   $148.46   $148.45   $148.50  
  Purchase #7 $111.56   12.604%   $125.621   $125.62   $125.60   $125.60  
  7 purchase totals = $1,119.92       $1,217.3260   $1,217.32   $1,217.25   $1,217.40