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	$15.27	4.204%	$15.912	$15.91	$15.90	$15.90
Purchase #2	$42.31	4.592%	$44.2529	$44.25	$44.25	$44.30
Purchase #3	$75.40	9.313%	$82.422	$82.42	$82.40	$82.40
Purchase #4	$148.39	13.630%	$168.6156	$168.62	$168.60	$168.60
Purchase #5	$88.27	13.146%	$99.874	$99.87	$99.85	$99.90
Purchase #6	$132.93	13.692%	$151.1308	$151.13	$151.15	$151.10
Purchase #7	$98.50	8.376%	$106.7504	$106.75	$106.75	$106.80
7 purchase totals =	$601.07		$668.9577	$668.95	$668.90	$669.00