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	$10.81	6.374%	$11.499	$11.50	$11.50	$11.50
Purchase #2	$83.94	3.608%	$86.9686	$86.97	$86.95	$87.00
Purchase #3	$214.88	12.845%	$242.4813	$242.48	$242.50	$242.50
Purchase #4	$78.43	13.606%	$89.1012	$89.10	$89.10	$89.10
Purchase #5	$237.55	5.729%	$251.1592	$251.16	$251.15	$251.20
Purchase #6	$74.30	5.400%	$78.3122	$78.31	$78.30	$78.30
Purchase #7	$37.93	5.191%	$39.8989	$39.90	$39.90	$39.90
7 purchase totals =	$737.84		$799.4204	$799.42	$799.40	$799.50