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	$151.26	11.288%	$168.3342	$168.33	$168.35	$168.30
Purchase #2	$145.81	4.660%	$152.6047	$152.60	$152.60	$152.60
Purchase #3	$221.25	8.534%	$240.1315	$240.13	$240.15	$240.10
Purchase #4	$53.79	9.853%	$59.0899	$59.09	$59.10	$59.10
Purchase #5	$23.84	9.329%	$26.064	$26.06	$26.05	$26.10
Purchase #6	$49.47	13.775%	$56.2845	$56.28	$56.30	$56.30
Purchase #7	$128.58	10.109%	$141.5782	$141.58	$141.60	$141.60
7 purchase totals =	$774.00		$844.0870	$844.07	$844.15	$844.10