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	$141.51	6.136%	$150.1931	$150.19	$150.20	$150.20
Purchase #2	$158.31	6.606%	$168.768	$168.77	$168.75	$168.80
Purchase #3	$169.94	9.762%	$186.5295	$186.53	$186.55	$186.50
Purchase #4	$161.89	13.510%	$183.7613	$183.76	$183.75	$183.80
Purchase #5	$77.94	8.520%	$84.5805	$84.58	$84.60	$84.60
Purchase #6	$177.72	11.601%	$198.3373	$198.34	$198.35	$198.30
Purchase #7	$98.40	13.325%	$111.5118	$111.51	$111.50	$111.50
7 purchase totals =	$985.71		$1,083.6815	$1,083.68	$1,083.70	$1,083.70