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	$212.53	4.692%	$222.5019	$222.50	$222.50	$222.50
Purchase #2	$117.42	13.274%	$133.0063	$133.01	$133.00	$133.00
Purchase #3	$169.93	13.521%	$192.9062	$192.91	$192.90	$192.90
Purchase #4	$153.35	7.792%	$165.299	$165.30	$165.30	$165.30
Purchase #5	$13.59	10.670%	$15.0401	$15.04	$15.05	$15.00
Purchase #6	$107.94	9.648%	$118.3541	$118.35	$118.35	$118.40
Purchase #7	$38.78	9.223%	$42.3567	$42.36	$42.35	$42.40
7 purchase totals =	$813.54		$889.4643	$889.47	$889.45	$889.50