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	$32.94	10.830%	$36.5074	$36.51	$36.50	$36.50
Purchase #2	$49.27	7.208%	$52.8214	$52.82	$52.80	$52.80
Purchase #3	$42.54	5.309%	$44.7984	$44.80	$44.80	$44.80
Purchase #4	$49.89	9.867%	$54.8126	$54.81	$54.80	$54.80
Purchase #5	$132.99	7.102%	$142.4349	$142.43	$142.45	$142.40
Purchase #6	$110.40	11.659%	$123.2715	$123.27	$123.25	$123.30
Purchase #7	$168.98	11.355%	$188.1677	$188.17	$188.15	$188.20
7 purchase totals =	$587.01		$642.8139	$642.81	$642.75	$642.80