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	$10.86	5.787%	$11.4885	$11.49	$11.50	$11.50
Purchase #2	$148.44	11.774%	$165.9173	$165.92	$165.90	$165.90
Purchase #3	$82.32	9.716%	$90.3182	$90.32	$90.30	$90.30
Purchase #4	$159.72	10.301%	$176.1728	$176.17	$176.15	$176.20
Purchase #5	$58.94	13.153%	$66.6924	$66.69	$66.70	$66.70
Purchase #6	$214.83	12.624%	$241.9501	$241.95	$241.95	$242.00
Purchase #7	$149.95	10.212%	$165.2629	$165.26	$165.25	$165.30
7 purchase totals =	$825.06		$917.8022	$917.80	$917.75	$917.90