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	$28.63	11.226%	$31.844	$31.84	$31.85	$31.80
Purchase #2	$40.82	3.181%	$42.1185	$42.12	$42.10	$42.10
Purchase #3	$75.65	10.501%	$83.594	$83.59	$83.60	$83.60
Purchase #4	$91.73	5.528%	$96.8008	$96.80	$96.80	$96.80
Purchase #5	$33.96	12.290%	$38.1337	$38.13	$38.15	$38.10
Purchase #6	$39.83	4.817%	$41.7486	$41.75	$41.75	$41.70
Purchase #7	$11.45	10.852%	$12.6926	$12.69	$12.70	$12.70
7 purchase totals =	$322.07		$346.9322	$346.92	$346.95	$346.80