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	$246.68	10.489%	$272.5543	$272.55	$272.55	$272.60
Purchase #2	$187.89	3.724%	$194.887	$194.89	$194.90	$194.90
Purchase #3	$52.30	6.132%	$55.507	$55.51	$55.50	$55.50
Purchase #4	$236.87	11.284%	$263.5984	$263.60	$263.60	$263.60
Purchase #5	$226.54	4.126%	$235.887	$235.89	$235.90	$235.90
Purchase #6	$142.49	8.806%	$155.0377	$155.04	$155.05	$155.00
Purchase #7	$20.44	10.191%	$22.523	$22.52	$22.50	$22.50
7 purchase totals =	$1,113.21		$1,199.9944	$1,200.00	$1,200.00	$1,200.00