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	$71.31	9.368%	$77.9903	$77.99	$78.00	$78.00
Purchase #2	$164.68	10.556%	$182.0636	$182.06	$182.05	$182.10
Purchase #3	$43.62	10.325%	$48.1238	$48.12	$48.10	$48.10
Purchase #4	$70.73	11.614%	$78.9446	$78.94	$78.95	$78.90
Purchase #5	$100.84	8.169%	$109.0776	$109.08	$109.10	$109.10
Purchase #6	$111.72	8.526%	$121.2452	$121.25	$121.25	$121.20
Purchase #7	$173.74	9.640%	$190.4885	$190.49	$190.50	$190.50
7 purchase totals =	$736.64		$807.9336	$807.93	$807.95	$807.90