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	$154.54	11.752%	$172.7015	$172.70	$172.70	$172.70
Purchase #2	$108.70	9.299%	$118.808	$118.81	$118.80	$118.80
Purchase #3	$233.53	13.364%	$264.7389	$264.74	$264.75	$264.70
Purchase #4	$146.46	12.191%	$164.3149	$164.31	$164.30	$164.30
Purchase #5	$62.39	5.181%	$65.6224	$65.62	$65.60	$65.60
Purchase #6	$77.32	6.451%	$82.3079	$82.31	$82.30	$82.30
Purchase #7	$15.29	7.395%	$16.4207	$16.42	$16.40	$16.40
7 purchase totals =	$798.23		$884.9143	$884.91	$884.85	$884.80