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	$82.86	4.822%	$86.8555	$86.86	$86.85	$86.90
Purchase #2	$102.64	12.766%	$115.743	$115.74	$115.75	$115.70
Purchase #3	$93.59	3.456%	$96.8245	$96.82	$96.80	$96.80
Purchase #4	$42.88	13.117%	$48.5046	$48.50	$48.50	$48.50
Purchase #5	$233.97	8.498%	$253.8528	$253.85	$253.85	$253.90
Purchase #6	$66.33	9.307%	$72.5033	$72.50	$72.50	$72.50
Purchase #7	$5.84	13.361%	$6.6203	$6.62	$6.60	$6.60
7 purchase totals =	$628.11		$680.9040	$680.89	$680.85	$680.90