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	$81.35	11.323%	$90.5613	$90.56	$90.55	$90.60
Purchase #2	$35.38	8.630%	$38.4333	$38.43	$38.45	$38.40
Purchase #3	$59.32	5.741%	$62.7256	$62.73	$62.75	$62.70
Purchase #4	$32.85	13.240%	$37.1993	$37.20	$37.20	$37.20
Purchase #5	$220.98	4.717%	$231.4036	$231.40	$231.40	$231.40
Purchase #6	$160.65	4.461%	$167.8166	$167.82	$167.80	$167.80
Purchase #7	$82.78	5.852%	$87.6243	$87.62	$87.60	$87.60
7 purchase totals =	$673.31		$715.7640	$715.76	$715.75	$715.70