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	$228.57	9.106%	$249.3836	$249.38	$249.40	$249.40
Purchase #2	$166.94	13.805%	$189.9861	$189.99	$190.00	$190.00
Purchase #3	$106.94	8.557%	$116.0909	$116.09	$116.10	$116.10
Purchase #4	$11.87	11.601%	$13.247	$13.25	$13.25	$13.20
Purchase #5	$42.67	9.225%	$46.6063	$46.61	$46.60	$46.60
Purchase #6	$99.90	3.683%	$103.5793	$103.58	$103.60	$103.60
Purchase #7	$116.45	9.645%	$127.6816	$127.68	$127.70	$127.70
7 purchase totals =	$773.34		$846.5748	$846.58	$846.65	$846.60