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	$159.34	12.863%	$179.8359	$179.84	$179.85	$179.80
Purchase #2	$229.66	7.204%	$246.2047	$246.20	$246.20	$246.20
Purchase #3	$34.67	10.267%	$38.2296	$38.23	$38.25	$38.20
Purchase #4	$123.46	3.218%	$127.4329	$127.43	$127.45	$127.40
Purchase #5	$52.85	3.386%	$54.6395	$54.64	$54.65	$54.60
Purchase #6	$185.87	7.275%	$199.392	$199.39	$199.40	$199.40
Purchase #7	$120.62	4.680%	$126.265	$126.27	$126.25	$126.30
7 purchase totals =	$906.47		$971.9996	$972.00	$972.05	$971.90