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	$37.44	12.599%	$42.1571	$42.16	$42.15	$42.20
Purchase #2	$162.41	6.184%	$172.4534	$172.45	$172.45	$172.50
Purchase #3	$179.69	4.405%	$187.6053	$187.61	$187.60	$187.60
Purchase #4	$165.42	4.495%	$172.8556	$172.86	$172.85	$172.90
Purchase #5	$202.43	11.516%	$225.7418	$225.74	$225.75	$225.70
Purchase #6	$201.44	6.304%	$214.1388	$214.14	$214.15	$214.10
Purchase #7	$219.42	6.286%	$233.2127	$233.21	$233.20	$233.20
7 purchase totals =	$1,168.25		$1,248.1647	$1,248.17	$1,248.15	$1,248.20