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	$11.83	9.374%	$12.9389	$12.94	$12.95	$12.90
Purchase #2	$55.91	5.850%	$59.1807	$59.18	$59.20	$59.20
Purchase #3	$64.93	10.525%	$71.7639	$71.76	$71.75	$71.80
Purchase #4	$69.76	6.167%	$74.0621	$74.06	$74.05	$74.10
Purchase #5	$105.87	3.510%	$109.586	$109.59	$109.60	$109.60
Purchase #6	$107.78	12.777%	$121.5511	$121.55	$121.55	$121.60
Purchase #7	$21.47	3.749%	$22.2749	$22.27	$22.25	$22.30
7 purchase totals =	$437.55		$471.3576	$471.35	$471.35	$471.50