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	$217.27	3.604%	$225.1004	$225.10	$225.10	$225.10
Purchase #2	$238.94	7.106%	$255.9191	$255.92	$255.90	$255.90
Purchase #3	$72.43	6.672%	$77.2625	$77.26	$77.25	$77.30
Purchase #4	$138.55	11.359%	$154.2879	$154.29	$154.30	$154.30
Purchase #5	$156.69	11.728%	$175.0666	$175.07	$175.05	$175.10
Purchase #6	$146.77	6.248%	$155.9402	$155.94	$155.95	$155.90
Purchase #7	$42.61	7.214%	$45.6839	$45.68	$45.70	$45.70
7 purchase totals =	$1,013.26		$1,089.2606	$1,089.26	$1,089.25	$1,089.30