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	$127.85	10.653%	$141.4699	$141.47	$141.45	$141.50
Purchase #2	$128.33	3.336%	$132.6111	$132.61	$132.60	$132.60
Purchase #3	$113.51	12.633%	$127.8497	$127.85	$127.85	$127.80
Purchase #4	$6.78	6.854%	$7.2447	$7.24	$7.25	$7.20
Purchase #5	$138.33	8.641%	$150.2831	$150.28	$150.30	$150.30
Purchase #6	$238.80	5.687%	$252.3806	$252.38	$252.40	$252.40
Purchase #7	$26.58	3.856%	$27.6049	$27.60	$27.60	$27.60
7 purchase totals =	$780.18		$839.4440	$839.43	$839.45	$839.40