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	$30.81	11.461%	$34.3411	$34.34	$34.35	$34.30
Purchase #2	$155.54	11.625%	$173.6215	$173.62	$173.60	$173.60
Purchase #3	$71.91	11.772%	$80.3752	$80.38	$80.40	$80.40
Purchase #4	$39.55	9.122%	$43.1578	$43.16	$43.15	$43.20
Purchase #5	$162.77	13.778%	$185.1965	$185.20	$185.20	$185.20
Purchase #6	$131.84	4.531%	$137.8137	$137.81	$137.80	$137.80
Purchase #7	$248.89	12.335%	$279.5906	$279.59	$279.60	$279.60
7 purchase totals =	$841.31		$934.0964	$934.10	$934.10	$934.10