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	$145.38	6.518%	$154.8559	$154.86	$154.85	$154.90
Purchase #2	$40.25	12.536%	$45.2957	$45.30	$45.30	$45.30
Purchase #3	$139.28	3.114%	$143.6172	$143.62	$143.60	$143.60
Purchase #4	$127.51	13.739%	$145.0286	$145.03	$145.05	$145.00
Purchase #5	$31.74	5.664%	$33.5378	$33.54	$33.55	$33.50
Purchase #6	$66.87	11.170%	$74.3394	$74.34	$74.35	$74.30
Purchase #7	$229.56	12.618%	$258.5259	$258.53	$258.55	$258.50
7 purchase totals =	$780.59		$855.2005	$855.22	$855.25	$855.10