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	$6.59	10.218%	$7.2634	$7.26	$7.25	$7.30
Purchase #2	$7.81	13.380%	$8.855	$8.86	$8.85	$8.90
Purchase #3	$172.69	3.410%	$178.5787	$178.58	$178.60	$178.60
Purchase #4	$172.59	13.869%	$196.5265	$196.53	$196.55	$196.50
Purchase #5	$246.54	11.828%	$275.7008	$275.70	$275.70	$275.70
Purchase #6	$237.32	7.359%	$254.7844	$254.78	$254.80	$254.80
Purchase #7	$17.30	9.643%	$18.9682	$18.97	$18.95	$19.00
7 purchase totals =	$860.84		$940.6770	$940.68	$940.70	$940.80