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	$64.75	12.186%	$72.6404	$72.64	$72.65	$72.60
Purchase #2	$116.78	9.421%	$127.7818	$127.78	$127.80	$127.80
Purchase #3	$147.44	6.729%	$157.3612	$157.36	$157.35	$157.40
Purchase #4	$111.88	13.842%	$127.3664	$127.37	$127.35	$127.40
Purchase #5	$110.50	12.375%	$124.1744	$124.17	$124.15	$124.20
Purchase #6	$39.37	6.123%	$41.7806	$41.78	$41.80	$41.80
Purchase #7	$214.74	5.397%	$226.3295	$226.33	$226.35	$226.30
7 purchase totals =	$805.46		$877.4343	$877.43	$877.45	$877.50