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 $62.59   13.666%   $71.1435   $71.14   $71.15   $71.10  
  Purchase #2 $93.39   9.166%   $101.9501   $101.95   $101.95   $102.00  
  Purchase #3 $233.55   9.231%   $255.109   $255.11   $255.10   $255.10  
  Purchase #4 $32.38   8.245%   $35.0497   $35.05   $35.05   $35.00  
  Purchase #5 $74.94   10.694%   $82.9541   $82.95   $82.95   $83.00  
  Purchase #6 $49.69   11.335%   $55.3224   $55.32   $55.30   $55.30  
  Purchase #7 $23.67   10.675%   $26.1968   $26.20   $26.20   $26.20  
  7 purchase totals = $570.21       $627.7256   $627.72   $627.70   $627.70