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	$92.78	13.372%	$105.1865	$105.19	$105.20	$105.20
Purchase #2	$62.90	6.388%	$66.9181	$66.92	$66.90	$66.90
Purchase #3	$184.58	13.357%	$209.2344	$209.23	$209.25	$209.20
Purchase #4	$170.68	4.697%	$178.6968	$178.70	$178.70	$178.70
Purchase #5	$88.47	13.555%	$100.4621	$100.46	$100.45	$100.50
Purchase #6	$190.65	9.325%	$208.4281	$208.43	$208.45	$208.40
Purchase #7	$38.72	6.700%	$41.3142	$41.31	$41.30	$41.30
7 purchase totals =	$828.78		$910.2402	$910.24	$910.25	$910.20