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	$41.29	3.189%	$42.6067	$42.61	$42.60	$42.60
Purchase #2	$244.50	4.409%	$255.28	$255.28	$255.30	$255.30
Purchase #3	$184.73	7.352%	$198.3113	$198.31	$198.30	$198.30
Purchase #4	$126.88	7.668%	$136.6092	$136.61	$136.60	$136.60
Purchase #5	$38.38	11.456%	$42.7768	$42.78	$42.80	$42.80
Purchase #6	$138.48	12.693%	$156.0573	$156.06	$156.05	$156.10
Purchase #7	$105.31	10.384%	$116.2454	$116.25	$116.25	$116.20
7 purchase totals =	$879.57		$947.8867	$947.90	$947.90	$947.90