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	$247.43	9.208%	$270.2134	$270.21	$270.20	$270.20
Purchase #2	$116.42	11.873%	$130.2425	$130.24	$130.25	$130.20
Purchase #3	$146.35	4.613%	$153.1011	$153.10	$153.10	$153.10
Purchase #4	$85.92	4.756%	$90.0064	$90.01	$90.00	$90.00
Purchase #5	$249.63	13.193%	$282.5637	$282.56	$282.55	$282.60
Purchase #6	$74.51	11.296%	$82.9266	$82.93	$82.95	$82.90
Purchase #7	$49.50	6.845%	$52.8883	$52.89	$52.90	$52.90
7 purchase totals =	$969.76		$1,061.9420	$1,061.94	$1,061.95	$1,061.90