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	$39.79	9.340%	$43.5064	$43.51	$43.50	$43.50
Purchase #2	$48.51	8.423%	$52.596	$52.60	$52.60	$52.60
Purchase #3	$125.78	8.834%	$136.8914	$136.89	$136.90	$136.90
Purchase #4	$130.46	9.540%	$142.9059	$142.91	$142.90	$142.90
Purchase #5	$107.27	3.630%	$111.1639	$111.16	$111.15	$111.20
Purchase #6	$193.58	7.326%	$207.7617	$207.76	$207.75	$207.80
Purchase #7	$222.68	9.506%	$243.848	$243.85	$243.85	$243.80
7 purchase totals =	$868.07		$938.6733	$938.68	$938.65	$938.70