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	$10.85	11.109%	$12.0553	$12.06	$12.05	$12.10
Purchase #2	$98.89	10.326%	$109.1014	$109.10	$109.10	$109.10
Purchase #3	$77.27	5.575%	$81.5778	$81.58	$81.60	$81.60
Purchase #4	$188.25	8.443%	$204.1439	$204.14	$204.15	$204.10
Purchase #5	$145.62	8.620%	$158.1724	$158.17	$158.15	$158.20
Purchase #6	$131.81	5.526%	$139.0938	$139.09	$139.10	$139.10
Purchase #7	$182.79	4.113%	$190.3082	$190.31	$190.30	$190.30
7 purchase totals =	$835.48		$894.4528	$894.45	$894.45	$894.50