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 $113.28   11.490%   $126.2959   $126.30   $126.30   $126.30  
  Purchase #2 $109.78   8.242%   $118.8281   $118.83   $118.85   $118.80  
  Purchase #3 $132.78   10.159%   $146.2691   $146.27   $146.25   $146.30  
  Purchase #4 $61.38   13.837%   $69.8732   $69.87   $69.85   $69.90  
  Purchase #5 $130.33   3.306%   $134.6387   $134.64   $134.65   $134.60  
  Purchase #6 $124.64   10.351%   $137.5415   $137.54   $137.55   $137.50  
  Purchase #7 $231.34   12.121%   $259.3807   $259.38   $259.40   $259.40  
  7 purchase totals = $903.53       $992.8272   $992.83   $992.85   $992.80