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	$249.38	11.757%	$278.6996	$278.70	$278.70	$278.70
Purchase #2	$134.26	4.625%	$140.4695	$140.47	$140.45	$140.50
Purchase #3	$138.32	9.153%	$150.9804	$150.98	$151.00	$151.00
Purchase #4	$148.50	4.777%	$155.5938	$155.59	$155.60	$155.60
Purchase #5	$140.84	4.804%	$147.606	$147.61	$147.60	$147.60
Purchase #6	$141.28	11.448%	$157.4537	$157.45	$157.45	$157.50
Purchase #7	$179.69	3.307%	$185.6323	$185.63	$185.65	$185.60
7 purchase totals =	$1,132.27		$1,216.4353	$1,216.43	$1,216.45	$1,216.50