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	$208.89	7.338%	$224.2183	$224.22	$224.20	$224.20
Purchase #2	$217.45	8.479%	$235.8876	$235.89	$235.90	$235.90
Purchase #3	$28.46	13.509%	$32.3047	$32.30	$32.30	$32.30
Purchase #4	$55.38	13.530%	$62.8729	$62.87	$62.85	$62.90
Purchase #5	$35.89	5.647%	$37.9167	$37.92	$37.90	$37.90
Purchase #6	$33.82	12.610%	$38.0847	$38.08	$38.10	$38.10
Purchase #7	$54.90	6.717%	$58.5876	$58.59	$58.60	$58.60
7 purchase totals =	$634.79		$689.8725	$689.87	$689.85	$689.90