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	$152.77	11.838%	$170.8549	$170.85	$170.85	$170.90
Purchase #2	$123.47	6.149%	$131.0622	$131.06	$131.05	$131.10
Purchase #3	$40.59	7.183%	$43.5056	$43.51	$43.50	$43.50
Purchase #4	$112.58	13.670%	$127.9697	$127.97	$127.95	$128.00
Purchase #5	$41.58	3.678%	$43.1093	$43.11	$43.10	$43.10
Purchase #6	$210.26	9.700%	$230.6552	$230.66	$230.65	$230.70
Purchase #7	$236.86	9.554%	$259.4896	$259.49	$259.50	$259.50
7 purchase totals =	$918.11		$1,006.6465	$1,006.65	$1,006.60	$1,006.80