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	$79.35	12.806%	$89.5116	$89.51	$89.50	$89.50
Purchase #2	$122.27	5.619%	$129.1404	$129.14	$129.15	$129.10
Purchase #3	$49.55	7.792%	$53.4109	$53.41	$53.40	$53.40
Purchase #4	$175.26	13.581%	$199.0621	$199.06	$199.05	$199.10
Purchase #5	$23.50	7.751%	$25.3215	$25.32	$25.30	$25.30
Purchase #6	$111.97	7.720%	$120.6141	$120.61	$120.60	$120.60
Purchase #7	$98.80	6.808%	$105.5263	$105.53	$105.55	$105.50
7 purchase totals =	$660.70		$722.5869	$722.58	$722.55	$722.50