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	$237.41	5.773%	$251.1157	$251.12	$251.10	$251.10
Purchase #2	$143.27	10.724%	$158.6343	$158.63	$158.65	$158.60
Purchase #3	$28.25	13.356%	$32.0231	$32.02	$32.00	$32.00
Purchase #4	$55.59	6.527%	$59.2184	$59.22	$59.20	$59.20
Purchase #5	$141.84	10.491%	$156.7204	$156.72	$156.70	$156.70
Purchase #6	$133.78	13.205%	$151.4456	$151.45	$151.45	$151.40
Purchase #7	$16.99	9.208%	$18.5544	$18.55	$18.55	$18.60
7 purchase totals =	$757.13		$827.7119	$827.71	$827.65	$827.60