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	$36.41	10.379%	$40.189	$40.19	$40.20	$40.20
Purchase #2	$229.35	4.341%	$239.3061	$239.31	$239.30	$239.30
Purchase #3	$121.72	4.652%	$127.3824	$127.38	$127.40	$127.40
Purchase #4	$153.86	12.447%	$173.011	$173.01	$173.00	$173.00
Purchase #5	$114.54	5.463%	$120.7973	$120.80	$120.80	$120.80
Purchase #6	$58.38	5.130%	$61.3749	$61.37	$61.35	$61.40
Purchase #7	$152.43	9.176%	$166.417	$166.42	$166.40	$166.40
7 purchase totals =	$866.69		$928.4777	$928.48	$928.45	$928.50