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 $245.83   5.584%   $259.5571   $259.56   $259.55   $259.60  
  Purchase #2 $33.86   3.675%   $35.1044   $35.10   $35.10   $35.10  
  Purchase #3 $159.80   7.338%   $171.5261   $171.53   $171.55   $171.50  
  Purchase #4 $6.26   13.363%   $7.0965   $7.10   $7.10   $7.10  
  Purchase #5 $113.99   3.853%   $118.382   $118.38   $118.40   $118.40  
  Purchase #6 $115.76   8.461%   $125.5545   $125.55   $125.55   $125.60  
  Purchase #7 $218.77   12.268%   $245.6087   $245.61   $245.60   $245.60  
  7 purchase totals = $894.27       $962.8293   $962.83   $962.85   $962.90