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	$106.77	7.258%	$114.5194	$114.52	$114.50	$114.50
Purchase #2	$9.25	13.536%	$10.5021	$10.50	$10.50	$10.50
Purchase #3	$250.61	11.498%	$279.4251	$279.43	$279.45	$279.40
Purchase #4	$193.89	3.406%	$200.4939	$200.49	$200.50	$200.50
Purchase #5	$52.88	8.144%	$57.1865	$57.19	$57.20	$57.20
Purchase #6	$54.45	6.709%	$58.1031	$58.10	$58.10	$58.10
Purchase #7	$65.96	12.578%	$74.2564	$74.26	$74.25	$74.30
7 purchase totals =	$733.81		$794.4865	$794.49	$794.50	$794.50