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	$46.89	7.743%	$50.5207	$50.52	$50.50	$50.50
Purchase #2	$106.55	6.493%	$113.4683	$113.47	$113.45	$113.50
Purchase #3	$173.31	3.507%	$179.388	$179.39	$179.40	$179.40
Purchase #4	$101.70	3.237%	$104.992	$104.99	$105.00	$105.00
Purchase #5	$100.37	11.445%	$111.8573	$111.86	$111.85	$111.90
Purchase #6	$246.46	3.735%	$255.6653	$255.67	$255.65	$255.70
Purchase #7	$52.29	10.300%	$57.6759	$57.68	$57.70	$57.70
7 purchase totals =	$827.57		$873.5675	$873.58	$873.55	$873.70