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	$207.88	12.262%	$233.3702	$233.37	$233.35	$233.40
Purchase #2	$123.60	11.682%	$138.039	$138.04	$138.05	$138.00
Purchase #3	$104.31	9.736%	$114.4656	$114.47	$114.45	$114.50
Purchase #4	$78.29	11.608%	$87.3779	$87.38	$87.40	$87.40
Purchase #5	$187.31	4.866%	$196.4245	$196.42	$196.40	$196.40
Purchase #6	$15.73	10.120%	$17.3219	$17.32	$17.30	$17.30
Purchase #7	$159.49	6.253%	$169.4629	$169.46	$169.45	$169.50
7 purchase totals =	$876.61		$956.4620	$956.46	$956.40	$956.50