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 $246.70   13.652%   $280.3795   $280.38   $280.40   $280.40  
  Purchase #2 $88.30   8.667%   $95.953   $95.95   $95.95   $96.00  
  Purchase #3 $110.84   12.182%   $124.3425   $124.34   $124.35   $124.30  
  Purchase #4 $78.84   3.564%   $81.6499   $81.65   $81.65   $81.60  
  Purchase #5 $109.98   5.259%   $115.7638   $115.76   $115.75   $115.80  
  Purchase #6 $77.63   11.784%   $86.7779   $86.78   $86.80   $86.80  
  Purchase #7 $239.29   7.139%   $256.3729   $256.37   $256.35   $256.40  
  7 purchase totals = $951.58       $1,041.2395   $1,041.23   $1,041.25   $1,041.30