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	$34.51	9.527%	$37.7978	$37.80	$37.80	$37.80
Purchase #2	$131.89	3.278%	$136.2134	$136.21	$136.20	$136.20
Purchase #3	$145.46	6.595%	$155.0531	$155.05	$155.05	$155.10
Purchase #4	$167.59	5.275%	$176.4304	$176.43	$176.45	$176.40
Purchase #5	$215.77	4.191%	$224.8129	$224.81	$224.80	$224.80
Purchase #6	$214.47	6.373%	$228.1382	$228.14	$228.15	$228.10
Purchase #7	$87.78	10.184%	$96.7195	$96.72	$96.70	$96.70
7 purchase totals =	$997.47		$1,055.1653	$1,055.16	$1,055.15	$1,055.10