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	$145.93	4.531%	$152.5421	$152.54	$152.55	$152.50
Purchase #2	$133.94	4.860%	$140.4495	$140.45	$140.45	$140.40
Purchase #3	$228.69	11.631%	$255.2889	$255.29	$255.30	$255.30
Purchase #4	$124.47	13.415%	$141.1677	$141.17	$141.15	$141.20
Purchase #5	$100.39	10.275%	$110.7051	$110.71	$110.70	$110.70
Purchase #6	$36.64	12.435%	$41.1962	$41.20	$41.20	$41.20
Purchase #7	$101.92	9.253%	$111.3507	$111.35	$111.35	$111.40
7 purchase totals =	$871.98		$952.7002	$952.71	$952.70	$952.70