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	$11.43	12.572%	$12.867	$12.87	$12.85	$12.90
Purchase #2	$228.84	5.724%	$241.9388	$241.94	$241.95	$241.90
Purchase #3	$140.88	11.856%	$157.5827	$157.58	$157.60	$157.60
Purchase #4	$203.72	9.224%	$222.5111	$222.51	$222.50	$222.50
Purchase #5	$41.63	7.665%	$44.8209	$44.82	$44.80	$44.80
Purchase #6	$48.51	4.297%	$50.5945	$50.59	$50.60	$50.60
Purchase #7	$243.61	13.753%	$277.1137	$277.11	$277.10	$277.10
7 purchase totals =	$918.62		$1,007.4287	$1,007.42	$1,007.40	$1,007.40