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	$81.27	10.387%	$89.7115	$89.71	$89.70	$89.70
Purchase #2	$102.87	4.451%	$107.4487	$107.45	$107.45	$107.40
Purchase #3	$78.51	6.123%	$83.3172	$83.32	$83.30	$83.30
Purchase #4	$210.43	3.796%	$218.4179	$218.42	$218.40	$218.40
Purchase #5	$172.46	8.197%	$186.5965	$186.60	$186.60	$186.60
Purchase #6	$166.42	3.516%	$172.2713	$172.27	$172.25	$172.30
Purchase #7	$198.99	7.189%	$213.2954	$213.30	$213.30	$213.30
7 purchase totals =	$1,010.95		$1,071.0585	$1,071.07	$1,071.00	$1,071.00