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	$21.45	5.370%	$22.6019	$22.60	$22.60	$22.60
Purchase #2	$211.49	7.466%	$227.2798	$227.28	$227.30	$227.30
Purchase #3	$50.67	11.183%	$56.3364	$56.34	$56.35	$56.30
Purchase #4	$165.77	13.514%	$188.1722	$188.17	$188.15	$188.20
Purchase #5	$43.55	4.617%	$45.5607	$45.56	$45.55	$45.60
Purchase #6	$104.87	7.512%	$112.7478	$112.75	$112.75	$112.70
Purchase #7	$169.33	10.195%	$186.5932	$186.59	$186.60	$186.60
7 purchase totals =	$767.13		$839.2920	$839.29	$839.30	$839.30