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	$196.72	6.213%	$208.9422	$208.94	$208.95	$208.90
Purchase #2	$83.41	5.659%	$88.1302	$88.13	$88.15	$88.10
Purchase #3	$17.32	5.386%	$18.2529	$18.25	$18.25	$18.30
Purchase #4	$210.58	7.817%	$227.041	$227.04	$227.05	$227.00
Purchase #5	$13.55	13.163%	$15.3336	$15.33	$15.35	$15.30
Purchase #6	$20.26	11.149%	$22.5188	$22.52	$22.50	$22.50
Purchase #7	$52.29	13.244%	$59.2153	$59.22	$59.20	$59.20
7 purchase totals =	$594.13		$639.4340	$639.43	$639.45	$639.30