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	$7.66	3.616%	$7.937	$7.94	$7.95	$7.90
Purchase #2	$137.78	5.247%	$145.0093	$145.01	$145.00	$145.00
Purchase #3	$120.39	10.257%	$132.7384	$132.74	$132.75	$132.70
Purchase #4	$44.81	4.768%	$46.9465	$46.95	$46.95	$46.90
Purchase #5	$112.50	9.855%	$123.5869	$123.59	$123.60	$123.60
Purchase #6	$81.76	10.574%	$90.4053	$90.41	$90.40	$90.40
Purchase #7	$82.28	5.229%	$86.5824	$86.58	$86.60	$86.60
7 purchase totals =	$587.18		$633.2058	$633.22	$633.25	$633.10