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	$20.66	10.777%	$22.8865	$22.89	$22.90	$22.90
Purchase #2	$141.54	5.868%	$149.8456	$149.85	$149.85	$149.80
Purchase #3	$223.26	13.388%	$253.15	$253.15	$253.15	$253.20
Purchase #4	$159.55	3.441%	$165.0401	$165.04	$165.05	$165.00
Purchase #5	$111.96	13.679%	$127.275	$127.28	$127.30	$127.30
Purchase #6	$72.45	3.222%	$74.7843	$74.78	$74.80	$74.80
Purchase #7	$115.68	7.649%	$124.5284	$124.53	$124.55	$124.50
7 purchase totals =	$845.10		$917.5099	$917.52	$917.60	$917.50