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	$37.39	5.462%	$39.4322	$39.43	$39.45	$39.40
Purchase #2	$31.87	10.324%	$35.1603	$35.16	$35.15	$35.20
Purchase #3	$153.69	8.620%	$166.9381	$166.94	$166.95	$166.90
Purchase #4	$210.77	10.799%	$233.5311	$233.53	$233.55	$233.50
Purchase #5	$82.43	11.761%	$92.1246	$92.12	$92.10	$92.10
Purchase #6	$247.85	4.718%	$259.5436	$259.54	$259.55	$259.50
Purchase #7	$150.67	13.493%	$170.9999	$171.00	$171.00	$171.00
7 purchase totals =	$914.67		$997.7298	$997.72	$997.75	$997.60