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	$247.35	13.312%	$280.2772	$280.28	$280.30	$280.30
Purchase #2	$86.26	4.502%	$90.1434	$90.14	$90.15	$90.10
Purchase #3	$51.31	3.187%	$52.9452	$52.95	$52.95	$52.90
Purchase #4	$33.37	13.323%	$37.8159	$37.82	$37.80	$37.80
Purchase #5	$212.44	12.475%	$238.9419	$238.94	$238.95	$238.90
Purchase #6	$9.86	12.171%	$11.0601	$11.06	$11.05	$11.10
Purchase #7	$190.64	7.520%	$204.9761	$204.98	$205.00	$205.00
7 purchase totals =	$831.23		$916.1598	$916.17	$916.20	$916.10