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	$67.60	10.178%	$74.4803	$74.48	$74.50	$74.50
Purchase #2	$135.66	11.828%	$151.7059	$151.71	$151.70	$151.70
Purchase #3	$133.28	5.612%	$140.7597	$140.76	$140.75	$140.80
Purchase #4	$82.50	8.323%	$89.3665	$89.37	$89.35	$89.40
Purchase #5	$106.29	5.347%	$111.9733	$111.97	$111.95	$112.00
Purchase #6	$147.88	13.155%	$167.3336	$167.33	$167.35	$167.30
Purchase #7	$56.44	7.606%	$60.7328	$60.73	$60.75	$60.70
7 purchase totals =	$729.65		$796.3521	$796.35	$796.35	$796.40