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	$249.79	8.541%	$271.1246	$271.12	$271.10	$271.10
Purchase #2	$114.32	11.775%	$127.7812	$127.78	$127.80	$127.80
Purchase #3	$228.69	4.302%	$238.5282	$238.53	$238.55	$238.50
Purchase #4	$121.83	12.724%	$137.3316	$137.33	$137.35	$137.30
Purchase #5	$85.40	6.540%	$90.9852	$90.99	$91.00	$91.00
Purchase #6	$127.62	3.510%	$132.0995	$132.10	$132.10	$132.10
Purchase #7	$191.74	10.803%	$212.4537	$212.45	$212.45	$212.50
7 purchase totals =	$1,119.39		$1,210.3040	$1,210.30	$1,210.35	$1,210.30