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	$54.49	8.850%	$59.3124	$59.31	$59.30	$59.30
Purchase #2	$165.62	13.693%	$188.2983	$188.30	$188.30	$188.30
Purchase #3	$89.42	12.168%	$100.3006	$100.30	$100.30	$100.30
Purchase #4	$20.47	7.657%	$22.0374	$22.04	$22.05	$22.00
Purchase #5	$159.58	8.637%	$173.3629	$173.36	$173.35	$173.40
Purchase #6	$216.86	5.232%	$228.2061	$228.21	$228.20	$228.20
Purchase #7	$94.57	7.762%	$101.9105	$101.91	$101.90	$101.90
7 purchase totals =	$801.01		$873.4282	$873.43	$873.40	$873.40