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 $219.95   10.804%   $243.7134   $243.71   $243.70   $243.70  
  Purchase #2 $122.96   12.113%   $137.8541   $137.85   $137.85   $137.90  
  Purchase #3 $148.38   3.344%   $153.3418   $153.34   $153.35   $153.30  
  Purchase #4 $57.95   13.591%   $65.826   $65.83   $65.85   $65.80  
  Purchase #5 $245.87   11.463%   $274.0541   $274.05   $274.05   $274.10  
  Purchase #6 $44.55   13.445%   $50.5397   $50.54   $50.55   $50.50  
  Purchase #7 $29.46   4.629%   $30.8237   $30.82   $30.80   $30.80  
  7 purchase totals = $869.12       $956.1528   $956.14   $956.15   $956.10