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	$24.34	12.218%	$27.3139	$27.31	$27.30	$27.30
Purchase #2	$144.88	10.591%	$160.2242	$160.22	$160.20	$160.20
Purchase #3	$68.70	11.378%	$76.5167	$76.52	$76.50	$76.50
Purchase #4	$173.72	13.242%	$196.724	$196.72	$196.70	$196.70
Purchase #5	$76.93	4.586%	$80.458	$80.46	$80.45	$80.50
Purchase #6	$161.48	12.316%	$181.3679	$181.37	$181.35	$181.40
Purchase #7	$20.45	6.347%	$21.748	$21.75	$21.75	$21.70
7 purchase totals =	$670.50		$744.3527	$744.35	$744.25	$744.30