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	$146.92	7.554%	$158.0183	$158.02	$158.00	$158.00
Purchase #2	$25.44	8.164%	$27.5169	$27.52	$27.50	$27.50
Purchase #3	$82.63	3.189%	$85.2651	$85.27	$85.25	$85.30
Purchase #4	$172.29	9.643%	$188.9039	$188.90	$188.90	$188.90
Purchase #5	$240.66	4.475%	$251.4295	$251.43	$251.45	$251.40
Purchase #6	$125.27	6.250%	$133.0994	$133.10	$133.10	$133.10
Purchase #7	$113.89	12.143%	$127.7197	$127.72	$127.70	$127.70
7 purchase totals =	$907.10		$971.9528	$971.96	$971.90	$971.90