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	$147.49	9.711%	$161.8128	$161.81	$161.80	$161.80
Purchase #2	$153.78	12.154%	$172.4704	$172.47	$172.45	$172.50
Purchase #3	$104.68	7.850%	$112.8974	$112.90	$112.90	$112.90
Purchase #4	$89.92	8.759%	$97.7961	$97.80	$97.80	$97.80
Purchase #5	$149.65	3.609%	$155.0509	$155.05	$155.05	$155.10
Purchase #6	$35.78	12.149%	$40.1269	$40.13	$40.15	$40.10
Purchase #7	$37.34	7.751%	$40.2342	$40.23	$40.25	$40.20
7 purchase totals =	$718.64		$780.3887	$780.39	$780.40	$780.40