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	$82.53	8.827%	$89.8149	$89.81	$89.80	$89.80
Purchase #2	$34.47	7.710%	$37.1276	$37.13	$37.15	$37.10
Purchase #3	$111.99	5.760%	$118.4406	$118.44	$118.45	$118.40
Purchase #4	$154.87	6.333%	$164.6779	$164.68	$164.70	$164.70
Purchase #5	$102.38	10.747%	$113.3828	$113.38	$113.40	$113.40
Purchase #6	$109.87	8.823%	$119.5638	$119.56	$119.55	$119.60
Purchase #7	$218.69	9.565%	$239.6077	$239.61	$239.60	$239.60
7 purchase totals =	$814.80		$882.6153	$882.61	$882.65	$882.60