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	$69.30	13.432%	$78.6084	$78.61	$78.60	$78.60
Purchase #2	$74.98	9.598%	$82.1766	$82.18	$82.20	$82.20
Purchase #3	$10.43	4.374%	$10.8862	$10.89	$10.90	$10.90
Purchase #4	$145.83	5.708%	$154.154	$154.15	$154.15	$154.20
Purchase #5	$209.45	7.504%	$225.1671	$225.17	$225.15	$225.20
Purchase #6	$111.80	5.299%	$117.7243	$117.72	$117.70	$117.70
Purchase #7	$15.54	3.619%	$16.1024	$16.10	$16.10	$16.10
7 purchase totals =	$637.33		$684.8190	$684.82	$684.80	$684.90