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	$69.69	12.482%	$78.3887	$78.39	$78.40	$78.40
Purchase #2	$121.80	13.154%	$137.8216	$137.82	$137.80	$137.80
Purchase #3	$125.26	5.512%	$132.1643	$132.16	$132.15	$132.20
Purchase #4	$128.58	13.536%	$145.9846	$145.98	$146.00	$146.00
Purchase #5	$74.55	5.674%	$78.78	$78.78	$78.80	$78.80
Purchase #6	$149.88	13.796%	$170.5574	$170.56	$170.55	$170.60
Purchase #7	$200.91	13.733%	$228.501	$228.50	$228.50	$228.50
7 purchase totals =	$870.67		$972.1976	$972.19	$972.20	$972.30