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	$200.51	12.332%	$225.2369	$225.24	$225.25	$225.20
Purchase #2	$203.39	7.335%	$218.3087	$218.31	$218.30	$218.30
Purchase #3	$196.83	5.789%	$208.2245	$208.22	$208.20	$208.20
Purchase #4	$9.52	6.371%	$10.1265	$10.13	$10.15	$10.10
Purchase #5	$53.67	11.152%	$59.6553	$59.66	$59.65	$59.70
Purchase #6	$104.92	8.715%	$114.0638	$114.06	$114.05	$114.10
Purchase #7	$144.77	7.564%	$155.7204	$155.72	$155.70	$155.70
7 purchase totals =	$913.61		$991.3361	$991.34	$991.30	$991.30