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	$68.86	5.851%	$72.889	$72.89	$72.90	$72.90
Purchase #2	$42.61	8.299%	$46.1462	$46.15	$46.15	$46.10
Purchase #3	$7.28	7.329%	$7.8136	$7.81	$7.80	$7.80
Purchase #4	$173.38	6.750%	$185.0832	$185.08	$185.10	$185.10
Purchase #5	$239.74	13.593%	$272.3279	$272.33	$272.35	$272.30
Purchase #6	$76.87	13.178%	$86.9999	$87.00	$87.00	$87.00
Purchase #7	$19.33	10.251%	$21.3115	$21.31	$21.30	$21.30
7 purchase totals =	$628.07		$692.5713	$692.57	$692.60	$692.50