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	$73.29	12.434%	$82.4029	$82.40	$82.40	$82.40
Purchase #2	$75.86	8.614%	$82.3946	$82.39	$82.40	$82.40
Purchase #3	$84.31	7.210%	$90.3888	$90.39	$90.40	$90.40
Purchase #4	$19.86	3.163%	$20.4882	$20.49	$20.50	$20.50
Purchase #5	$143.52	10.393%	$158.436	$158.44	$158.45	$158.40
Purchase #6	$39.69	13.788%	$45.1625	$45.16	$45.15	$45.20
Purchase #7	$52.34	9.455%	$57.2887	$57.29	$57.30	$57.30
7 purchase totals =	$488.87		$536.5617	$536.56	$536.60	$536.60