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 $216.99   13.634%   $246.5744   $246.57   $246.55   $246.60  
  Purchase #2 $10.55   4.280%   $11.0015   $11.00   $11.00   $11.00  
  Purchase #3 $98.90   13.516%   $112.2673   $112.27   $112.25   $112.30  
  Purchase #4 $200.63   8.134%   $216.9492   $216.95   $216.95   $216.90  
  Purchase #5 $128.95   13.723%   $146.6458   $146.65   $146.65   $146.60  
  Purchase #6 $111.59   5.539%   $117.771   $117.77   $117.75   $117.80  
  Purchase #7 $18.46   8.197%   $19.9732   $19.97   $19.95   $20.00  
  7 purchase totals = $786.07       $871.1824   $871.18   $871.10   $871.20