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	$151.95	4.362%	$158.5781	$158.58	$158.60	$158.60
Purchase #2	$79.68	3.495%	$82.4648	$82.46	$82.45	$82.50
Purchase #3	$220.75	3.416%	$228.2908	$228.29	$228.30	$228.30
Purchase #4	$53.41	9.172%	$58.3088	$58.31	$58.30	$58.30
Purchase #5	$173.46	4.865%	$181.8988	$181.90	$181.90	$181.90
Purchase #6	$54.89	12.254%	$61.6162	$61.62	$61.60	$61.60
Purchase #7	$31.56	3.617%	$32.7015	$32.70	$32.70	$32.70
7 purchase totals =	$765.70		$803.8590	$803.86	$803.85	$803.90