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	$11.31	11.621%	$12.6243	$12.62	$12.60	$12.60
Purchase #2	$130.46	4.355%	$136.1415	$136.14	$136.15	$136.10
Purchase #3	$137.78	6.268%	$146.4161	$146.42	$146.40	$146.40
Purchase #4	$193.55	12.497%	$217.7379	$217.74	$217.75	$217.70
Purchase #5	$133.69	4.640%	$139.8932	$139.89	$139.90	$139.90
Purchase #6	$180.26	10.695%	$199.5388	$199.54	$199.55	$199.50
Purchase #7	$122.58	7.291%	$131.5173	$131.52	$131.50	$131.50
7 purchase totals =	$909.63		$983.8691	$983.87	$983.85	$983.70