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	$156.72	9.782%	$172.0504	$172.05	$172.05	$172.10
Purchase #2	$123.71	5.602%	$130.6402	$130.64	$130.65	$130.60
Purchase #3	$107.36	7.267%	$115.1619	$115.16	$115.15	$115.20
Purchase #4	$139.54	13.779%	$158.7672	$158.77	$158.75	$158.80
Purchase #5	$152.54	10.323%	$168.2867	$168.29	$168.30	$168.30
Purchase #6	$31.48	4.230%	$32.8116	$32.81	$32.80	$32.80
Purchase #7	$158.91	13.631%	$180.571	$180.57	$180.55	$180.60
7 purchase totals =	$870.26		$958.2890	$958.29	$958.25	$958.40