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	$118.85	3.734%	$123.2879	$123.29	$123.30	$123.30
Purchase #2	$99.38	12.135%	$111.4398	$111.44	$111.45	$111.40
Purchase #3	$249.57	9.225%	$272.5928	$272.59	$272.60	$272.60
Purchase #4	$45.99	5.128%	$48.3484	$48.35	$48.35	$48.30
Purchase #5	$203.26	4.753%	$212.9209	$212.92	$212.90	$212.90
Purchase #6	$176.58	12.545%	$198.732	$198.73	$198.75	$198.70
Purchase #7	$87.52	11.430%	$97.5235	$97.52	$97.50	$97.50
7 purchase totals =	$981.15		$1,064.8453	$1,064.84	$1,064.85	$1,064.70