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	$107.72	3.269%	$111.2414	$111.24	$111.25	$111.20
Purchase #2	$245.90	4.521%	$257.0171	$257.02	$257.00	$257.00
Purchase #3	$204.36	7.440%	$219.5644	$219.56	$219.55	$219.60
Purchase #4	$76.52	5.390%	$80.6444	$80.64	$80.65	$80.60
Purchase #5	$160.33	3.856%	$166.5123	$166.51	$166.50	$166.50
Purchase #6	$198.56	12.104%	$222.5937	$222.59	$222.60	$222.60
Purchase #7	$226.35	11.480%	$252.335	$252.34	$252.35	$252.30
7 purchase totals =	$1,219.74		$1,309.9083	$1,309.90	$1,309.90	$1,309.80