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	$83.61	8.331%	$90.5755	$90.58	$90.60	$90.60
Purchase #2	$186.93	4.436%	$195.2222	$195.22	$195.20	$195.20
Purchase #3	$78.91	9.205%	$86.1737	$86.17	$86.15	$86.20
Purchase #4	$62.69	5.852%	$66.3586	$66.36	$66.35	$66.40
Purchase #5	$226.85	13.224%	$256.8486	$256.85	$256.85	$256.80
Purchase #6	$22.54	9.851%	$24.7604	$24.76	$24.75	$24.80
Purchase #7	$11.59	7.464%	$12.4551	$12.46	$12.45	$12.50
7 purchase totals =	$673.12		$732.3941	$732.40	$732.35	$732.50