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	$248.78	6.377%	$264.6447	$264.64	$264.65	$264.60
Purchase #2	$40.81	5.443%	$43.0313	$43.03	$43.05	$43.00
Purchase #3	$205.68	12.259%	$230.8943	$230.89	$230.90	$230.90
Purchase #4	$207.48	8.380%	$224.8668	$224.87	$224.85	$224.90
Purchase #5	$103.60	7.653%	$111.5285	$111.53	$111.55	$111.50
Purchase #6	$184.59	4.536%	$192.963	$192.96	$192.95	$193.00
Purchase #7	$196.65	10.614%	$217.5224	$217.52	$217.50	$217.50
7 purchase totals =	$1,187.59		$1,285.4510	$1,285.44	$1,285.45	$1,285.40