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	$149.59	11.239%	$166.4024	$166.40	$166.40	$166.40
Purchase #2	$17.30	4.777%	$18.1264	$18.13	$18.15	$18.10
Purchase #3	$93.81	12.212%	$105.2661	$105.27	$105.25	$105.30
Purchase #4	$48.40	10.700%	$53.5788	$53.58	$53.60	$53.60
Purchase #5	$33.34	10.493%	$36.8384	$36.84	$36.85	$36.80
Purchase #6	$66.28	7.395%	$71.1814	$71.18	$71.20	$71.20
Purchase #7	$19.49	7.753%	$21.0011	$21.00	$21.00	$21.00
7 purchase totals =	$428.21		$472.3946	$472.40	$472.45	$472.40