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	$45.74	6.297%	$48.6202	$48.62	$48.60	$48.60
Purchase #2	$19.89	10.169%	$21.9126	$21.91	$21.90	$21.90
Purchase #3	$34.50	8.754%	$37.5201	$37.52	$37.50	$37.50
Purchase #4	$55.26	5.460%	$58.2772	$58.28	$58.30	$58.30
Purchase #5	$146.84	7.449%	$157.7781	$157.78	$157.80	$157.80
Purchase #6	$32.59	12.234%	$36.5771	$36.58	$36.60	$36.60
Purchase #7	$61.94	5.493%	$65.3424	$65.34	$65.35	$65.30
7 purchase totals =	$396.76		$426.0277	$426.03	$426.05	$426.00