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	$116.95	6.286%	$124.3015	$124.30	$124.30	$124.30
Purchase #2	$80.82	10.625%	$89.4071	$89.41	$89.40	$89.40
Purchase #3	$145.44	8.603%	$157.9522	$157.95	$157.95	$158.00
Purchase #4	$159.48	11.658%	$178.0722	$178.07	$178.05	$178.10
Purchase #5	$63.49	5.281%	$66.8429	$66.84	$66.85	$66.80
Purchase #6	$89.53	12.247%	$100.4947	$100.49	$100.50	$100.50
Purchase #7	$94.50	11.494%	$105.3618	$105.36	$105.35	$105.40
7 purchase totals =	$750.21		$822.4324	$822.42	$822.40	$822.50