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	$83.37	4.778%	$87.3534	$87.35	$87.35	$87.40
Purchase #2	$38.83	11.694%	$43.3708	$43.37	$43.35	$43.40
Purchase #3	$38.79	11.339%	$43.1884	$43.19	$43.20	$43.20
Purchase #4	$231.45	10.127%	$254.8889	$254.89	$254.90	$254.90
Purchase #5	$157.91	5.262%	$166.2192	$166.22	$166.20	$166.20
Purchase #6	$96.44	11.527%	$107.5566	$107.56	$107.55	$107.60
Purchase #7	$172.52	13.799%	$196.326	$196.33	$196.35	$196.30
7 purchase totals =	$819.31		$898.9033	$898.91	$898.90	$899.00