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	$171.66	6.116%	$182.1587	$182.16	$182.15	$182.20
Purchase #2	$45.66	9.729%	$50.1023	$50.10	$50.10	$50.10
Purchase #3	$168.44	3.116%	$173.6886	$173.69	$173.70	$173.70
Purchase #4	$40.39	7.728%	$43.5113	$43.51	$43.50	$43.50
Purchase #5	$138.25	10.272%	$152.451	$152.45	$152.45	$152.50
Purchase #6	$11.54	13.549%	$13.1036	$13.10	$13.10	$13.10
Purchase #7	$48.65	12.325%	$54.6461	$54.65	$54.65	$54.60
7 purchase totals =	$624.59		$669.6616	$669.66	$669.65	$669.70