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	$19.81	10.359%	$21.8621	$21.86	$21.85	$21.90
Purchase #2	$225.56	3.649%	$233.7907	$233.79	$233.80	$233.80
Purchase #3	$28.25	4.387%	$29.4893	$29.49	$29.50	$29.50
Purchase #4	$229.30	6.208%	$243.5349	$243.53	$243.55	$243.50
Purchase #5	$32.67	5.846%	$34.5799	$34.58	$34.60	$34.60
Purchase #6	$226.83	13.382%	$257.1844	$257.18	$257.20	$257.20
Purchase #7	$164.59	10.535%	$181.9296	$181.93	$181.95	$181.90
7 purchase totals =	$927.01		$1,002.3709	$1,002.36	$1,002.45	$1,002.40