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	$11.72	8.126%	$12.6724	$12.67	$12.65	$12.70
Purchase #2	$48.84	12.122%	$54.7604	$54.76	$54.75	$54.80
Purchase #3	$192.51	9.508%	$210.8139	$210.81	$210.80	$210.80
Purchase #4	$19.56	3.561%	$20.2565	$20.26	$20.25	$20.30
Purchase #5	$49.33	4.365%	$51.4833	$51.48	$51.50	$51.50
Purchase #6	$131.46	10.344%	$145.0582	$145.06	$145.05	$145.10
Purchase #7	$149.41	12.608%	$168.2476	$168.25	$168.25	$168.20
7 purchase totals =	$602.83		$663.2923	$663.29	$663.25	$663.40