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	$208.78	10.425%	$230.5453	$230.55	$230.55	$230.50
Purchase #2	$132.78	11.703%	$148.3192	$148.32	$148.30	$148.30
Purchase #3	$103.28	13.501%	$117.2238	$117.22	$117.20	$117.20
Purchase #4	$6.58	8.740%	$7.1551	$7.16	$7.15	$7.20
Purchase #5	$137.48	3.807%	$142.7139	$142.71	$142.70	$142.70
Purchase #6	$79.73	12.381%	$89.6014	$89.60	$89.60	$89.60
Purchase #7	$26.26	4.138%	$27.3466	$27.35	$27.35	$27.30
7 purchase totals =	$694.89		$762.9053	$762.91	$762.85	$762.80