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	$19.52	3.322%	$20.1685	$20.17	$20.15	$20.20
Purchase #2	$164.60	4.635%	$172.2292	$172.23	$172.25	$172.20
Purchase #3	$158.60	3.532%	$164.2018	$164.20	$164.20	$164.20
Purchase #4	$12.53	4.502%	$13.0941	$13.09	$13.10	$13.10
Purchase #5	$68.62	6.809%	$73.2923	$73.29	$73.30	$73.30
Purchase #6	$170.57	5.379%	$179.745	$179.75	$179.75	$179.70
Purchase #7	$78.57	13.829%	$89.4354	$89.44	$89.45	$89.40
7 purchase totals =	$673.01		$712.1663	$712.17	$712.20	$712.10