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	$46.59	7.711%	$50.1826	$50.18	$50.20	$50.20
Purchase #2	$72.93	10.849%	$80.8422	$80.84	$80.85	$80.80
Purchase #3	$46.64	11.428%	$51.97	$51.97	$51.95	$52.00
Purchase #4	$182.60	7.656%	$196.5799	$196.58	$196.60	$196.60
Purchase #5	$219.60	3.757%	$227.8504	$227.85	$227.85	$227.90
Purchase #6	$19.91	12.772%	$22.4529	$22.45	$22.45	$22.50
Purchase #7	$153.67	9.230%	$167.8537	$167.85	$167.85	$167.90
7 purchase totals =	$741.94		$797.7317	$797.72	$797.75	$797.90