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 $104.57   13.532%   $118.7204   $118.72   $118.70   $118.70  
  Purchase #2 $129.99   4.577%   $135.9396   $135.94   $135.95   $135.90  
  Purchase #3 $133.36   8.687%   $144.945   $144.95   $144.95   $144.90  
  Purchase #4 $137.67   6.479%   $146.5896   $146.59   $146.60   $146.60  
  Purchase #5 $91.59   6.160%   $97.2319   $97.23   $97.25   $97.20  
  Purchase #6 $128.86   3.425%   $133.2735   $133.27   $133.25   $133.30  
  Purchase #7 $189.90   10.702%   $210.2231   $210.22   $210.20   $210.20  
  7 purchase totals = $915.94       $986.9231   $986.92   $986.90   $986.80