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	$29.39	4.411%	$30.6864	$30.69	$30.70	$30.70
Purchase #2	$65.80	10.178%	$72.4971	$72.50	$72.50	$72.50
Purchase #3	$137.29	9.141%	$149.8397	$149.84	$149.85	$149.80
Purchase #4	$172.26	11.852%	$192.6763	$192.68	$192.70	$192.70
Purchase #5	$157.85	11.238%	$175.5892	$175.59	$175.60	$175.60
Purchase #6	$73.72	5.526%	$77.7938	$77.79	$77.80	$77.80
Purchase #7	$86.32	3.643%	$89.4646	$89.46	$89.45	$89.50
7 purchase totals =	$722.63		$788.5471	$788.55	$788.60	$788.60