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	$109.91	6.364%	$116.9047	$116.90	$116.90	$116.90
Purchase #2	$58.66	6.704%	$62.5926	$62.59	$62.60	$62.60
Purchase #3	$235.46	11.212%	$261.8598	$261.86	$261.85	$261.90
Purchase #4	$197.83	9.536%	$216.6951	$216.70	$216.70	$216.70
Purchase #5	$143.87	5.245%	$151.416	$151.42	$151.40	$151.40
Purchase #6	$53.68	13.270%	$60.8033	$60.80	$60.80	$60.80
Purchase #7	$107.33	4.241%	$111.8819	$111.88	$111.90	$111.90
7 purchase totals =	$906.74		$982.1534	$982.15	$982.15	$982.20