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	$29.94	6.453%	$31.872	$31.87	$31.85	$31.90
Purchase #2	$192.52	4.102%	$200.4172	$200.42	$200.40	$200.40
Purchase #3	$148.97	10.410%	$164.4778	$164.48	$164.50	$164.50
Purchase #4	$100.38	13.587%	$114.0186	$114.02	$114.00	$114.00
Purchase #5	$192.52	8.215%	$208.3355	$208.34	$208.35	$208.30
Purchase #6	$238.27	12.810%	$268.7924	$268.79	$268.80	$268.80
Purchase #7	$43.49	10.248%	$47.9469	$47.95	$47.95	$47.90
7 purchase totals =	$946.09		$1,035.8604	$1,035.87	$1,035.85	$1,035.80