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	$112.78	9.319%	$123.29	$123.29	$123.30	$123.30
Purchase #2	$173.86	12.862%	$196.2219	$196.22	$196.20	$196.20
Purchase #3	$201.85	7.729%	$217.451	$217.45	$217.45	$217.50
Purchase #4	$179.78	11.698%	$200.8107	$200.81	$200.80	$200.80
Purchase #5	$25.86	4.515%	$27.0276	$27.03	$27.05	$27.00
Purchase #6	$250.89	12.206%	$281.5136	$281.51	$281.50	$281.50
Purchase #7	$186.85	11.813%	$208.9226	$208.92	$208.90	$208.90
7 purchase totals =	$1,131.87		$1,255.2374	$1,255.23	$1,255.20	$1,255.20