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	$145.97	5.114%	$153.4349	$153.43	$153.45	$153.40
Purchase #2	$142.98	13.159%	$161.7947	$161.79	$161.80	$161.80
Purchase #3	$90.94	10.338%	$100.3414	$100.34	$100.35	$100.30
Purchase #4	$143.86	9.838%	$158.0129	$158.01	$158.00	$158.00
Purchase #5	$171.82	8.623%	$186.636	$186.64	$186.65	$186.60
Purchase #6	$43.69	6.689%	$46.6124	$46.61	$46.60	$46.60
Purchase #7	$22.28	11.656%	$24.877	$24.88	$24.90	$24.90
7 purchase totals =	$761.54		$831.7093	$831.70	$831.75	$831.60