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	$79.39	13.123%	$89.8083	$89.81	$89.80	$89.80
Purchase #2	$52.32	6.469%	$55.7046	$55.70	$55.70	$55.70
Purchase #3	$111.37	13.501%	$126.4061	$126.41	$126.40	$126.40
Purchase #4	$139.80	9.643%	$153.2809	$153.28	$153.30	$153.30
Purchase #5	$92.76	13.422%	$105.2102	$105.21	$105.20	$105.20
Purchase #6	$40.39	5.392%	$42.5678	$42.57	$42.55	$42.60
Purchase #7	$44.41	10.740%	$49.1796	$49.18	$49.20	$49.20
7 purchase totals =	$560.44		$622.1575	$622.16	$622.15	$622.20