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	$53.82	10.200%	$59.3096	$59.31	$59.30	$59.30
Purchase #2	$53.34	11.490%	$59.4688	$59.47	$59.45	$59.50
Purchase #3	$86.34	8.384%	$93.5787	$93.58	$93.60	$93.60
Purchase #4	$13.59	10.266%	$14.9851	$14.99	$15.00	$15.00
Purchase #5	$53.88	10.416%	$59.4921	$59.49	$59.50	$59.50
Purchase #6	$162.32	3.622%	$168.1992	$168.20	$168.20	$168.20
Purchase #7	$212.75	10.411%	$234.8994	$234.90	$234.90	$234.90
7 purchase totals =	$636.04		$689.9329	$689.94	$689.95	$690.00