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	$35.31	13.861%	$40.2043	$40.20	$40.20	$40.20
Purchase #2	$58.49	6.795%	$62.4644	$62.46	$62.45	$62.50
Purchase #3	$183.94	4.742%	$192.6624	$192.66	$192.65	$192.70
Purchase #4	$108.89	13.149%	$123.2079	$123.21	$123.20	$123.20
Purchase #5	$131.75	11.504%	$146.9065	$146.91	$146.90	$146.90
Purchase #6	$185.45	11.376%	$206.5468	$206.55	$206.55	$206.50
Purchase #7	$63.48	11.725%	$70.923	$70.92	$70.90	$70.90
7 purchase totals =	$767.31		$842.9153	$842.91	$842.85	$842.90