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 $56.50   10.864%   $62.6382   $62.64   $62.65   $62.60  
  Purchase #2 $98.71   3.149%   $101.8184   $101.82   $101.80   $101.80  
  Purchase #3 $230.51   6.855%   $246.3115   $246.31   $246.30   $246.30  
  Purchase #4 $52.69   8.734%   $57.2919   $57.29   $57.30   $57.30  
  Purchase #5 $9.38   11.175%   $10.4282   $10.43   $10.45   $10.40  
  Purchase #6 $208.85   3.298%   $215.7379   $215.74   $215.75   $215.70  
  Purchase #7 $143.66   11.534%   $160.2297   $160.23   $160.25   $160.20  
  7 purchase totals = $800.30       $854.4558   $854.46   $854.50   $854.30