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	$128.83	13.779%	$146.5815	$146.58	$146.60	$146.60
Purchase #2	$33.68	3.645%	$34.9076	$34.91	$34.90	$34.90
Purchase #3	$196.75	10.867%	$218.1308	$218.13	$218.15	$218.10
Purchase #4	$239.86	11.136%	$266.5708	$266.57	$266.55	$266.60
Purchase #5	$225.55	3.622%	$233.7194	$233.72	$233.70	$233.70
Purchase #6	$173.90	6.419%	$185.0626	$185.06	$185.05	$185.10
Purchase #7	$132.70	5.155%	$139.5407	$139.54	$139.55	$139.50
7 purchase totals =	$1,131.27		$1,224.5134	$1,224.51	$1,224.50	$1,224.50