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	$56.67	8.348%	$61.4008	$61.40	$61.40	$61.40
Purchase #2	$240.97	13.774%	$274.1612	$274.16	$274.15	$274.20
Purchase #3	$95.46	6.724%	$101.8787	$101.88	$101.90	$101.90
Purchase #4	$44.95	7.102%	$48.1423	$48.14	$48.15	$48.10
Purchase #5	$131.40	7.721%	$141.5454	$141.55	$141.55	$141.50
Purchase #6	$29.47	6.705%	$31.446	$31.45	$31.45	$31.40
Purchase #7	$45.85	8.822%	$49.8949	$49.89	$49.90	$49.90
7 purchase totals =	$644.77		$708.4693	$708.47	$708.50	$708.40