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 $239.93   5.583%   $253.3253   $253.33   $253.35   $253.30  
  Purchase #2 $202.87   7.284%   $217.6471   $217.65   $217.65   $217.60  
  Purchase #3 $59.54   4.392%   $62.155   $62.16   $62.15   $62.20  
  Purchase #4 $7.54   5.602%   $7.9624   $7.96   $7.95   $8.00  
  Purchase #5 $125.99   8.809%   $137.0885   $137.09   $137.10   $137.10  
  Purchase #6 $140.77   5.782%   $148.9093   $148.91   $148.90   $148.90  
  Purchase #7 $167.41   6.672%   $178.5796   $178.58   $178.60   $178.60  
  7 purchase totals = $944.05       $1,005.6672   $1,005.68   $1,005.70   $1,005.70