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	$140.93	12.547%	$158.6125	$158.61	$158.60	$158.60
Purchase #2	$164.88	9.116%	$179.9105	$179.91	$179.90	$179.90
Purchase #3	$131.45	13.214%	$148.8198	$148.82	$148.80	$148.80
Purchase #4	$242.52	12.302%	$272.3548	$272.35	$272.35	$272.40
Purchase #5	$31.43	6.457%	$33.4594	$33.46	$33.45	$33.50
Purchase #6	$186.83	4.691%	$195.5942	$195.59	$195.60	$195.60
Purchase #7	$102.68	8.463%	$111.3698	$111.37	$111.35	$111.40
7 purchase totals =	$1,000.72		$1,100.1210	$1,100.11	$1,100.05	$1,100.20