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	$120.99	13.740%	$137.614	$137.61	$137.60	$137.60
Purchase #2	$200.65	13.695%	$228.129	$228.13	$228.15	$228.10
Purchase #3	$81.85	10.745%	$90.6448	$90.64	$90.65	$90.60
Purchase #4	$45.65	5.506%	$48.1635	$48.16	$48.15	$48.20
Purchase #5	$222.29	4.843%	$233.0555	$233.06	$233.05	$233.10
Purchase #6	$59.98	3.567%	$62.1195	$62.12	$62.10	$62.10
Purchase #7	$108.66	11.166%	$120.793	$120.79	$120.80	$120.80
7 purchase totals =	$840.07		$920.5193	$920.51	$920.50	$920.50