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	$156.29	5.722%	$165.2329	$165.23	$165.25	$165.20
Purchase #2	$112.62	12.845%	$127.086	$127.09	$127.10	$127.10
Purchase #3	$142.73	4.107%	$148.5919	$148.59	$148.60	$148.60
Purchase #4	$27.45	11.291%	$30.5494	$30.55	$30.55	$30.50
Purchase #5	$61.60	8.648%	$66.9272	$66.93	$66.95	$66.90
Purchase #6	$139.66	7.648%	$150.3412	$150.34	$150.35	$150.30
Purchase #7	$237.96	13.671%	$270.4915	$270.49	$270.50	$270.50
7 purchase totals =	$878.31		$959.2201	$959.22	$959.30	$959.10