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	$11.89	13.746%	$13.5244	$13.52	$13.50	$13.50
Purchase #2	$88.90	9.484%	$97.3313	$97.33	$97.35	$97.30
Purchase #3	$180.69	3.186%	$186.4468	$186.45	$186.45	$186.40
Purchase #4	$83.73	6.162%	$88.8894	$88.89	$88.90	$88.90
Purchase #5	$118.47	12.692%	$133.5062	$133.51	$133.50	$133.50
Purchase #6	$54.68	12.618%	$61.5795	$61.58	$61.60	$61.60
Purchase #7	$75.46	8.137%	$81.6002	$81.60	$81.60	$81.60
7 purchase totals =	$613.82		$662.8778	$662.88	$662.90	$662.80