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 $219.98   11.121%   $244.444   $244.44   $244.45   $244.40  
  Purchase #2 $242.75   6.197%   $257.7932   $257.79   $257.80   $257.80  
  Purchase #3 $55.80   4.653%   $58.3964   $58.40   $58.40   $58.40  
  Purchase #4 $61.74   3.728%   $64.0417   $64.04   $64.05   $64.00  
  Purchase #5 $183.88   5.798%   $194.5414   $194.54   $194.55   $194.50  
  Purchase #6 $76.48   8.633%   $83.0825   $83.08   $83.10   $83.10  
  Purchase #7 $19.94   8.840%   $21.7027   $21.70   $21.70   $21.70  
  7 purchase totals = $860.57       $924.0019   $923.99   $924.05   $923.90