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 $48.67   13.783%   $55.3782   $55.38   $55.40   $55.40  
  Purchase #2 $241.78   4.721%   $253.1944   $253.19   $253.20   $253.20  
  Purchase #3 $175.83   4.250%   $183.3028   $183.30   $183.30   $183.30  
  Purchase #4 $103.71   11.521%   $115.6584   $115.66   $115.65   $115.70  
  Purchase #5 $129.93   5.867%   $137.553   $137.55   $137.55   $137.60  
  Purchase #6 $55.76   12.292%   $62.614   $62.61   $62.60   $62.60  
  Purchase #7 $91.75   4.854%   $96.2035   $96.20   $96.20   $96.20  
  7 purchase totals = $847.43       $903.9043   $903.89   $903.90   $904.00