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	$132.41	13.284%	$149.9993	$150.00	$150.00	$150.00
Purchase #2	$131.37	7.575%	$141.3213	$141.32	$141.30	$141.30
Purchase #3	$161.79	8.865%	$176.1327	$176.13	$176.15	$176.10
Purchase #4	$115.35	10.704%	$127.6971	$127.70	$127.70	$127.70
Purchase #5	$229.71	11.401%	$255.8992	$255.90	$255.90	$255.90
Purchase #6	$115.52	10.732%	$127.9176	$127.92	$127.90	$127.90
Purchase #7	$196.60	6.737%	$209.8449	$209.84	$209.85	$209.80
7 purchase totals =	$1,082.75		$1,188.8121	$1,188.81	$1,188.80	$1,188.70