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 $229.68   7.125%   $246.0447   $246.04   $246.05   $246.00  
  Purchase #2 $140.43   7.523%   $150.9945   $150.99   $151.00   $151.00  
  Purchase #3 $65.65   7.299%   $70.4418   $70.44   $70.45   $70.40  
  Purchase #4 $96.35   8.144%   $104.1967   $104.20   $104.20   $104.20  
  Purchase #5 $154.54   3.177%   $159.4497   $159.45   $159.45   $159.40  
  Purchase #6 $71.90   5.727%   $76.0177   $76.02   $76.00   $76.00  
  Purchase #7 $58.67   4.551%   $61.3401   $61.34   $61.35   $61.30  
  7 purchase totals = $817.22       $868.4852   $868.48   $868.50   $868.30