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	$54.25	7.472%	$58.3036	$58.30	$58.30	$58.30
Purchase #2	$107.49	3.719%	$111.4876	$111.49	$111.50	$111.50
Purchase #3	$75.70	4.450%	$79.0687	$79.07	$79.05	$79.10
Purchase #4	$172.55	3.236%	$178.1337	$178.13	$178.15	$178.10
Purchase #5	$214.44	12.512%	$241.2707	$241.27	$241.25	$241.30
Purchase #6	$37.50	12.824%	$42.309	$42.31	$42.30	$42.30
Purchase #7	$108.72	4.352%	$113.4515	$113.45	$113.45	$113.50
7 purchase totals =	$770.65		$824.0248	$824.02	$824.00	$824.10