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 $194.48   8.281%   $210.5849   $210.58   $210.60   $210.60  
  Purchase #2 $30.97   13.390%   $35.1169   $35.12   $35.10   $35.10  
  Purchase #3 $150.60   5.829%   $159.3785   $159.38   $159.40   $159.40  
  Purchase #4 $218.66   6.385%   $232.6214   $232.62   $232.60   $232.60  
  Purchase #5 $63.58   13.104%   $71.9115   $71.91   $71.90   $71.90  
  Purchase #6 $155.70   11.346%   $173.3657   $173.37   $173.35   $173.40  
  Purchase #7 $68.69   7.606%   $73.9146   $73.91   $73.90   $73.90  
  7 purchase totals = $882.68       $956.8935   $956.89   $956.85   $956.90