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	$175.39	4.605%	$183.4667	$183.47	$183.45	$183.50
Purchase #2	$39.38	3.830%	$40.8883	$40.89	$40.90	$40.90
Purchase #3	$105.55	6.643%	$112.5617	$112.56	$112.55	$112.60
Purchase #4	$241.43	12.418%	$271.4108	$271.41	$271.40	$271.40
Purchase #5	$191.42	10.657%	$211.8196	$211.82	$211.80	$211.80
Purchase #6	$218.83	4.304%	$228.2484	$228.25	$228.25	$228.20
Purchase #7	$164.38	5.424%	$173.296	$173.30	$173.30	$173.30
7 purchase totals =	$1,136.38		$1,221.6915	$1,221.70	$1,221.65	$1,221.70