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	$230.43	3.217%	$237.8429	$237.84	$237.85	$237.80
Purchase #2	$75.60	10.448%	$83.4987	$83.50	$83.50	$83.50
Purchase #3	$147.63	12.862%	$166.6182	$166.62	$166.60	$166.60
Purchase #4	$184.84	12.786%	$208.4736	$208.47	$208.45	$208.50
Purchase #5	$164.93	12.732%	$185.9289	$185.93	$185.95	$185.90
Purchase #6	$47.25	12.738%	$53.2687	$53.27	$53.25	$53.30
Purchase #7	$59.72	6.828%	$63.7977	$63.80	$63.80	$63.80
7 purchase totals =	$910.40		$999.4287	$999.43	$999.40	$999.40