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	$73.94	6.194%	$78.5198	$78.52	$78.50	$78.50
Purchase #2	$158.65	3.532%	$164.2535	$164.25	$164.25	$164.30
Purchase #3	$183.60	12.631%	$206.7905	$206.79	$206.80	$206.80
Purchase #4	$74.43	10.290%	$82.0888	$82.09	$82.10	$82.10
Purchase #5	$203.78	12.390%	$229.0283	$229.03	$229.05	$229.00
Purchase #6	$171.51	9.868%	$188.4346	$188.43	$188.45	$188.40
Purchase #7	$214.48	5.179%	$225.5879	$225.59	$225.60	$225.60
7 purchase totals =	$1,080.39		$1,174.7034	$1,174.70	$1,174.75	$1,174.70