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	$101.59	6.364%	$108.0552	$108.06	$108.05	$108.10
Purchase #2	$120.54	7.117%	$129.1188	$129.12	$129.10	$129.10
Purchase #3	$125.61	10.268%	$138.5076	$138.51	$138.50	$138.50
Purchase #4	$134.66	6.517%	$143.4358	$143.44	$143.45	$143.40
Purchase #5	$105.72	5.597%	$111.6371	$111.64	$111.65	$111.60
Purchase #6	$82.33	11.522%	$91.8161	$91.82	$91.80	$91.80
Purchase #7	$244.72	5.874%	$259.0949	$259.09	$259.10	$259.10
7 purchase totals =	$915.17		$981.6655	$981.68	$981.65	$981.60