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	$174.27	8.786%	$189.5814	$189.58	$189.60	$189.60
Purchase #2	$151.93	13.317%	$172.1625	$172.16	$172.15	$172.20
Purchase #3	$52.44	12.272%	$58.8754	$58.88	$58.90	$58.90
Purchase #4	$38.78	10.267%	$42.7615	$42.76	$42.75	$42.80
Purchase #5	$132.92	10.822%	$147.3046	$147.30	$147.30	$147.30
Purchase #6	$25.71	10.695%	$28.4597	$28.46	$28.45	$28.50
Purchase #7	$143.37	13.238%	$162.3493	$162.35	$162.35	$162.30
7 purchase totals =	$719.42		$801.4944	$801.49	$801.50	$801.60