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	$171.96	8.361%	$186.3376	$186.34	$186.35	$186.30
Purchase #2	$152.44	5.792%	$161.2693	$161.27	$161.25	$161.30
Purchase #3	$213.70	3.697%	$221.6005	$221.60	$221.60	$221.60
Purchase #4	$111.65	7.631%	$120.17	$120.17	$120.15	$120.20
Purchase #5	$38.94	13.674%	$44.2647	$44.26	$44.25	$44.30
Purchase #6	$160.88	7.109%	$172.317	$172.32	$172.30	$172.30
Purchase #7	$146.63	12.823%	$165.4324	$165.43	$165.45	$165.40
7 purchase totals =	$996.20		$1,071.3915	$1,071.39	$1,071.35	$1,071.40