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	$107.50	10.308%	$118.5811	$118.58	$118.60	$118.60
Purchase #2	$250.28	7.719%	$269.5991	$269.60	$269.60	$269.60
Purchase #3	$68.31	6.178%	$72.5302	$72.53	$72.55	$72.50
Purchase #4	$63.34	5.105%	$66.5735	$66.57	$66.55	$66.60
Purchase #5	$175.89	9.496%	$192.5925	$192.59	$192.60	$192.60
Purchase #6	$41.37	4.225%	$43.1179	$43.12	$43.10	$43.10
Purchase #7	$25.37	7.700%	$27.3235	$27.32	$27.30	$27.30
7 purchase totals =	$732.06		$790.3178	$790.31	$790.30	$790.30