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	$237.32	5.451%	$250.2563	$250.26	$250.25	$250.30
Purchase #2	$153.86	3.272%	$158.8943	$158.89	$158.90	$158.90
Purchase #3	$234.83	3.550%	$243.1665	$243.17	$243.15	$243.20
Purchase #4	$177.62	6.252%	$188.7248	$188.72	$188.70	$188.70
Purchase #5	$234.39	13.848%	$266.8483	$266.85	$266.85	$266.80
Purchase #6	$20.72	12.285%	$23.2655	$23.27	$23.25	$23.30
Purchase #7	$50.87	6.406%	$54.1287	$54.13	$54.15	$54.10
7 purchase totals =	$1,109.61		$1,185.2844	$1,185.29	$1,185.25	$1,185.30