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	$53.93	10.188%	$59.4244	$59.42	$59.40	$59.40
Purchase #2	$131.29	11.651%	$146.5866	$146.59	$146.60	$146.60
Purchase #3	$238.40	13.389%	$270.3194	$270.32	$270.30	$270.30
Purchase #4	$128.70	13.861%	$146.5391	$146.54	$146.55	$146.50
Purchase #5	$207.69	13.185%	$235.0739	$235.07	$235.05	$235.10
Purchase #6	$111.58	7.254%	$119.674	$119.67	$119.65	$119.70
Purchase #7	$172.57	8.842%	$187.8286	$187.83	$187.85	$187.80
7 purchase totals =	$1,044.16		$1,165.4460	$1,165.44	$1,165.40	$1,165.40