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 $246.43   4.526%   $257.5834   $257.58   $257.60   $257.60  
  Purchase #2 $100.38   11.307%   $111.73   $111.73   $111.75   $111.70  
  Purchase #3 $28.82   3.163%   $29.7316   $29.73   $29.75   $29.70  
  Purchase #4 $127.36   4.451%   $133.0288   $133.03   $133.05   $133.00  
  Purchase #5 $123.59   7.453%   $132.8012   $132.80   $132.80   $132.80  
  Purchase #6 $195.93   12.632%   $220.6799   $220.68   $220.70   $220.70  
  Purchase #7 $59.98   10.660%   $66.3739   $66.37   $66.35   $66.40  
  7 purchase totals = $882.49       $951.9288   $951.92   $952.00   $951.90