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	$20.99	6.129%	$22.2765	$22.28	$22.30	$22.30
Purchase #2	$112.58	9.396%	$123.158	$123.16	$123.15	$123.20
Purchase #3	$18.90	7.802%	$20.3746	$20.37	$20.35	$20.40
Purchase #4	$40.27	8.217%	$43.579	$43.58	$43.60	$43.60
Purchase #5	$35.30	11.812%	$39.4696	$39.47	$39.45	$39.50
Purchase #6	$136.70	7.200%	$146.5424	$146.54	$146.55	$146.50
Purchase #7	$127.54	7.664%	$137.3147	$137.31	$137.30	$137.30
7 purchase totals =	$492.28		$532.7148	$532.71	$532.70	$532.80