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	$29.94	5.688%	$31.643	$31.64	$31.65	$31.60
Purchase #2	$30.51	12.180%	$34.2261	$34.23	$34.25	$34.20
Purchase #3	$28.29	3.213%	$29.199	$29.20	$29.20	$29.20
Purchase #4	$29.91	10.844%	$33.1534	$33.15	$33.15	$33.20
Purchase #5	$10.81	11.542%	$12.0577	$12.06	$12.05	$12.10
Purchase #6	$80.46	11.613%	$89.8038	$89.80	$89.80	$89.80
Purchase #7	$216.28	13.513%	$245.5059	$245.51	$245.50	$245.50
7 purchase totals =	$426.20		$475.5889	$475.59	$475.60	$475.60