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	$186.40	9.170%	$203.4929	$203.49	$203.50	$203.50
Purchase #2	$158.83	11.186%	$176.5967	$176.60	$176.60	$176.60
Purchase #3	$229.47	12.653%	$258.5048	$258.50	$258.50	$258.50
Purchase #4	$216.48	5.223%	$227.7868	$227.79	$227.80	$227.80
Purchase #5	$179.73	4.782%	$188.3247	$188.32	$188.30	$188.30
Purchase #6	$86.35	4.312%	$90.0734	$90.07	$90.05	$90.10
Purchase #7	$126.37	13.575%	$143.5247	$143.52	$143.50	$143.50
7 purchase totals =	$1,183.63		$1,288.3040	$1,288.29	$1,288.25	$1,288.30