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	$38.72	3.458%	$40.0589	$40.06	$40.05	$40.10
Purchase #2	$75.95	13.861%	$86.4774	$86.48	$86.50	$86.50
Purchase #3	$13.67	9.487%	$14.9669	$14.97	$14.95	$15.00
Purchase #4	$123.25	3.123%	$127.0991	$127.10	$127.10	$127.10
Purchase #5	$221.95	11.320%	$247.0747	$247.07	$247.05	$247.10
Purchase #6	$103.42	13.232%	$117.1045	$117.10	$117.10	$117.10
Purchase #7	$172.62	10.282%	$190.3688	$190.37	$190.35	$190.40
7 purchase totals =	$749.58		$823.1503	$823.15	$823.10	$823.30