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	$47.69	13.417%	$54.0886	$54.09	$54.10	$54.10
Purchase #2	$238.97	13.655%	$271.6014	$271.60	$271.60	$271.60
Purchase #3	$30.82	9.133%	$33.6348	$33.63	$33.65	$33.60
Purchase #4	$35.38	5.616%	$37.3669	$37.37	$37.35	$37.40
Purchase #5	$47.94	9.500%	$52.4943	$52.49	$52.50	$52.50
Purchase #6	$61.27	8.788%	$66.6544	$66.65	$66.65	$66.70
Purchase #7	$46.47	9.251%	$50.7689	$50.77	$50.75	$50.80
7 purchase totals =	$508.54		$566.6093	$566.60	$566.60	$566.70