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	$20.30	6.685%	$21.6571	$21.66	$21.65	$21.70
Purchase #2	$153.41	5.850%	$162.3845	$162.38	$162.40	$162.40
Purchase #3	$63.44	13.854%	$72.229	$72.23	$72.25	$72.20
Purchase #4	$24.44	10.457%	$26.9957	$27.00	$27.00	$27.00
Purchase #5	$21.48	12.598%	$24.1861	$24.19	$24.20	$24.20
Purchase #6	$182.72	3.104%	$188.3916	$188.39	$188.40	$188.40
Purchase #7	$178.34	3.449%	$184.4909	$184.49	$184.50	$184.50
7 purchase totals =	$644.13		$680.3349	$680.34	$680.40	$680.40