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	$103.71	7.837%	$111.8378	$111.84	$111.85	$111.80
Purchase #2	$86.66	4.653%	$90.6923	$90.69	$90.70	$90.70
Purchase #3	$121.84	13.729%	$138.5674	$138.57	$138.55	$138.60
Purchase #4	$25.38	4.757%	$26.5873	$26.59	$26.60	$26.60
Purchase #5	$57.94	6.401%	$61.6487	$61.65	$61.65	$61.60
Purchase #6	$158.45	13.467%	$179.7885	$179.79	$179.80	$179.80
Purchase #7	$167.61	10.660%	$185.4772	$185.48	$185.50	$185.50
7 purchase totals =	$721.59		$794.5992	$794.61	$794.65	$794.60