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	$82.36	8.632%	$89.4693	$89.47	$89.45	$89.50
Purchase #2	$52.31	4.413%	$54.6184	$54.62	$54.60	$54.60
Purchase #3	$203.86	10.510%	$225.2857	$225.29	$225.30	$225.30
Purchase #4	$35.60	11.421%	$39.6659	$39.67	$39.65	$39.70
Purchase #5	$108.42	12.686%	$122.1742	$122.17	$122.15	$122.20
Purchase #6	$202.86	7.678%	$218.4356	$218.44	$218.45	$218.40
Purchase #7	$237.36	6.413%	$252.5819	$252.58	$252.60	$252.60
7 purchase totals =	$922.77		$1,002.2310	$1,002.24	$1,002.20	$1,002.30