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	$54.30	9.660%	$59.5454	$59.55	$59.55	$59.50
Purchase #2	$127.52	7.671%	$137.3021	$137.30	$137.30	$137.30
Purchase #3	$146.64	7.694%	$157.9225	$157.92	$157.90	$157.90
Purchase #4	$116.48	4.510%	$121.7332	$121.73	$121.75	$121.70
Purchase #5	$152.44	13.705%	$173.3319	$173.33	$173.35	$173.30
Purchase #6	$31.98	6.456%	$34.0446	$34.04	$34.05	$34.00
Purchase #7	$151.56	13.700%	$172.3237	$172.32	$172.30	$172.30
7 purchase totals =	$780.92		$856.2034	$856.19	$856.20	$856.00