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	$125.29	11.589%	$139.8099	$139.81	$139.80	$139.80
Purchase #2	$74.88	4.251%	$78.0631	$78.06	$78.05	$78.10
Purchase #3	$39.57	10.247%	$43.6247	$43.62	$43.60	$43.60
Purchase #4	$15.38	11.594%	$17.1632	$17.16	$17.15	$17.20
Purchase #5	$232.82	3.253%	$240.3936	$240.39	$240.40	$240.40
Purchase #6	$43.36	10.439%	$47.8864	$47.89	$47.90	$47.90
Purchase #7	$57.42	6.652%	$61.2396	$61.24	$61.25	$61.20
7 purchase totals =	$588.72		$628.1805	$628.17	$628.15	$628.20