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	$15.76	11.472%	$17.568	$17.57	$17.55	$17.60
Purchase #2	$44.28	13.228%	$50.1374	$50.14	$50.15	$50.10
Purchase #3	$140.25	8.415%	$152.052	$152.05	$152.05	$152.10
Purchase #4	$155.69	7.533%	$167.4181	$167.42	$167.40	$167.40
Purchase #5	$139.34	4.102%	$145.0557	$145.06	$145.05	$145.10
Purchase #6	$37.93	6.824%	$40.5183	$40.52	$40.50	$40.50
Purchase #7	$202.64	10.740%	$224.4035	$224.40	$224.40	$224.40
7 purchase totals =	$735.89		$797.1530	$797.16	$797.10	$797.20