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	$19.27	5.518%	$20.3333	$20.33	$20.35	$20.30
Purchase #2	$185.86	13.636%	$211.2039	$211.20	$211.20	$211.20
Purchase #3	$119.37	10.794%	$132.2548	$132.25	$132.25	$132.30
Purchase #4	$132.74	5.398%	$139.9053	$139.91	$139.90	$139.90
Purchase #5	$118.52	3.848%	$123.0806	$123.08	$123.10	$123.10
Purchase #6	$184.58	10.368%	$203.7173	$203.72	$203.70	$203.70
Purchase #7	$244.89	5.719%	$258.8953	$258.90	$258.90	$258.90
7 purchase totals =	$1,005.23		$1,089.3905	$1,089.39	$1,089.40	$1,089.40