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	$10.29	6.141%	$10.9219	$10.92	$10.90	$10.90
Purchase #2	$46.41	4.815%	$48.6446	$48.64	$48.65	$48.60
Purchase #3	$246.71	8.345%	$267.2979	$267.30	$267.30	$267.30
Purchase #4	$93.37	12.530%	$105.0693	$105.07	$105.05	$105.10
Purchase #5	$85.43	13.347%	$96.8323	$96.83	$96.85	$96.80
Purchase #6	$222.92	8.531%	$241.9373	$241.94	$241.95	$241.90
Purchase #7	$38.47	5.852%	$40.7213	$40.72	$40.70	$40.70
7 purchase totals =	$743.60		$811.4246	$811.42	$811.40	$811.30