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	$186.64	6.170%	$198.1557	$198.16	$198.15	$198.20
Purchase #2	$106.61	11.252%	$118.6058	$118.61	$118.60	$118.60
Purchase #3	$108.62	8.783%	$118.1601	$118.16	$118.15	$118.20
Purchase #4	$172.79	13.675%	$196.419	$196.42	$196.40	$196.40
Purchase #5	$134.45	9.124%	$146.7172	$146.72	$146.70	$146.70
Purchase #6	$200.34	9.800%	$219.9733	$219.97	$219.95	$220.00
Purchase #7	$55.81	13.772%	$63.4962	$63.50	$63.50	$63.50
7 purchase totals =	$965.26		$1,061.5273	$1,061.54	$1,061.45	$1,061.60