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 $59.90   8.522%   $65.0047   $65.00   $65.00   $65.00  
  Purchase #2 $113.30   12.685%   $127.6721   $127.67   $127.65   $127.70  
  Purchase #3 $157.84   9.806%   $173.3178   $173.32   $173.30   $173.30  
  Purchase #4 $12.88   13.510%   $14.6201   $14.62   $14.60   $14.60  
  Purchase #5 $144.88   5.602%   $152.9962   $153.00   $153.00   $153.00  
  Purchase #6 $180.63   4.177%   $188.1749   $188.17   $188.15   $188.20  
  Purchase #7 $32.36   8.849%   $35.2235   $35.22   $35.20   $35.20  
  7 purchase totals = $701.79       $757.0093   $757.00   $756.90   $757.00