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	$150.47	11.522%	$167.8072	$167.81	$167.80	$167.80
Purchase #2	$172.45	10.591%	$190.7142	$190.71	$190.70	$190.70
Purchase #3	$250.34	11.218%	$278.4231	$278.42	$278.40	$278.40
Purchase #4	$103.88	13.398%	$117.7978	$117.80	$117.80	$117.80
Purchase #5	$159.46	4.244%	$166.2275	$166.23	$166.25	$166.20
Purchase #6	$241.83	12.496%	$272.0491	$272.05	$272.05	$272.00
Purchase #7	$145.73	3.153%	$150.3249	$150.32	$150.30	$150.30
7 purchase totals =	$1,224.16		$1,343.3438	$1,343.34	$1,343.30	$1,343.20