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	$209.49	3.324%	$216.4534	$216.45	$216.45	$216.50
Purchase #2	$67.93	9.400%	$74.3154	$74.32	$74.30	$74.30
Purchase #3	$211.90	12.789%	$238.9999	$239.00	$239.00	$239.00
Purchase #4	$177.51	10.745%	$196.5834	$196.58	$196.60	$196.60
Purchase #5	$172.67	8.203%	$186.8341	$186.83	$186.85	$186.80
Purchase #6	$57.49	6.826%	$61.4143	$61.41	$61.40	$61.40
Purchase #7	$218.90	13.452%	$248.3464	$248.35	$248.35	$248.30
7 purchase totals =	$1,115.89		$1,222.9469	$1,222.94	$1,222.95	$1,222.90