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	$60.29	9.566%	$66.0573	$66.06	$66.05	$66.10
Purchase #2	$93.48	13.191%	$105.8109	$105.81	$105.80	$105.80
Purchase #3	$60.95	6.385%	$64.8417	$64.84	$64.85	$64.80
Purchase #4	$212.59	4.709%	$222.6009	$222.60	$222.60	$222.60
Purchase #5	$136.92	4.600%	$143.2183	$143.22	$143.20	$143.20
Purchase #6	$103.82	13.126%	$117.4474	$117.45	$117.45	$117.40
Purchase #7	$12.42	6.503%	$13.2277	$13.23	$13.25	$13.20
7 purchase totals =	$680.47		$733.2042	$733.21	$733.20	$733.10