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	$243.88	12.550%	$274.4869	$274.49	$274.50	$274.50
Purchase #2	$182.94	6.681%	$195.1622	$195.16	$195.15	$195.20
Purchase #3	$10.54	9.102%	$11.4994	$11.50	$11.50	$11.50
Purchase #4	$153.45	5.505%	$161.8974	$161.90	$161.90	$161.90
Purchase #5	$200.42	11.126%	$222.7187	$222.72	$222.70	$222.70
Purchase #6	$38.60	5.171%	$40.596	$40.60	$40.60	$40.60
Purchase #7	$69.48	7.845%	$74.9307	$74.93	$74.95	$74.90
7 purchase totals =	$899.31		$981.2913	$981.30	$981.30	$981.30