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 $22.66   11.584%   $25.2849   $25.28   $25.30   $25.30  
  Purchase #2 $155.80   6.788%   $166.3757   $166.38   $166.40   $166.40  
  Purchase #3 $119.85   5.360%   $126.274   $126.27   $126.25   $126.30  
  Purchase #4 $22.71   8.305%   $24.5961   $24.60   $24.60   $24.60  
  Purchase #5 $181.99   4.728%   $190.5945   $190.59   $190.60   $190.60  
  Purchase #6 $58.63   4.175%   $61.0778   $61.08   $61.10   $61.10  
  Purchase #7 $239.45   6.714%   $255.5267   $255.53   $255.55   $255.50  
  7 purchase totals = $801.09       $849.7297   $849.73   $849.80   $849.80