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	$89.72	12.137%	$100.6093	$100.61	$100.60	$100.60
Purchase #2	$225.99	6.517%	$240.7178	$240.72	$240.70	$240.70
Purchase #3	$166.43	3.870%	$172.8708	$172.87	$172.85	$172.90
Purchase #4	$88.26	3.835%	$91.6448	$91.64	$91.65	$91.60
Purchase #5	$67.45	4.264%	$70.3261	$70.33	$70.35	$70.30
Purchase #6	$206.26	9.157%	$225.1472	$225.15	$225.15	$225.10
Purchase #7	$144.92	6.177%	$153.8717	$153.87	$153.85	$153.90
7 purchase totals =	$989.03		$1,055.1877	$1,055.19	$1,055.15	$1,055.10