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	$121.77	10.533%	$134.596	$134.60	$134.60	$134.60
Purchase #2	$145.91	12.518%	$164.175	$164.18	$164.20	$164.20
Purchase #3	$82.35	9.266%	$89.9806	$89.98	$90.00	$90.00
Purchase #4	$135.73	7.201%	$145.5039	$145.50	$145.50	$145.50
Purchase #5	$16.72	10.379%	$18.4554	$18.46	$18.45	$18.50
Purchase #6	$116.37	4.320%	$121.3972	$121.40	$121.40	$121.40
Purchase #7	$59.65	8.339%	$64.6242	$64.62	$64.60	$64.60
7 purchase totals =	$678.50		$738.7323	$738.74	$738.75	$738.80