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	$119.71	6.704%	$127.7354	$127.74	$127.75	$127.70
Purchase #2	$52.85	8.776%	$57.4881	$57.49	$57.50	$57.50
Purchase #3	$145.79	5.333%	$153.565	$153.57	$153.55	$153.60
Purchase #4	$157.59	12.288%	$176.9547	$176.95	$176.95	$177.00
Purchase #5	$18.50	13.147%	$20.9322	$20.93	$20.95	$20.90
Purchase #6	$57.60	6.407%	$61.2904	$61.29	$61.30	$61.30
Purchase #7	$188.34	6.533%	$200.6443	$200.64	$200.65	$200.60
7 purchase totals =	$740.38		$798.6101	$798.61	$798.65	$798.60