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	$10.37	7.592%	$11.1573	$11.16	$11.15	$11.20
Purchase #2	$136.27	8.465%	$147.8053	$147.81	$147.80	$147.80
Purchase #3	$60.71	8.618%	$65.942	$65.94	$65.95	$65.90
Purchase #4	$146.91	13.278%	$166.4167	$166.42	$166.40	$166.40
Purchase #5	$132.66	13.478%	$150.5399	$150.54	$150.55	$150.50
Purchase #6	$73.87	6.193%	$78.4448	$78.44	$78.45	$78.40
Purchase #7	$94.92	10.135%	$104.5401	$104.54	$104.55	$104.50
7 purchase totals =	$655.71		$724.8461	$724.85	$724.85	$724.70