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	$222.58	13.168%	$251.8893	$251.89	$251.90	$251.90
Purchase #2	$200.96	4.779%	$210.5639	$210.56	$210.55	$210.60
Purchase #3	$13.78	6.487%	$14.6739	$14.67	$14.65	$14.70
Purchase #4	$72.75	5.825%	$76.9877	$76.99	$77.00	$77.00
Purchase #5	$62.93	12.554%	$70.8302	$70.83	$70.85	$70.80
Purchase #6	$151.94	11.628%	$169.6076	$169.61	$169.60	$169.60
Purchase #7	$75.44	4.569%	$78.8869	$78.89	$78.90	$78.90
7 purchase totals =	$800.38		$873.4395	$873.44	$873.45	$873.50