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	$70.75	10.798%	$78.3896	$78.39	$78.40	$78.40
Purchase #2	$59.55	12.764%	$67.151	$67.15	$67.15	$67.20
Purchase #3	$59.94	11.130%	$66.6113	$66.61	$66.60	$66.60
Purchase #4	$109.87	12.345%	$123.4335	$123.43	$123.45	$123.40
Purchase #5	$38.82	12.465%	$43.6589	$43.66	$43.65	$43.70
Purchase #6	$147.32	3.368%	$152.2817	$152.28	$152.30	$152.30
Purchase #7	$14.37	11.866%	$16.0751	$16.08	$16.10	$16.10
7 purchase totals =	$500.62		$547.6011	$547.60	$547.65	$547.70