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	$64.95	3.192%	$67.0232	$67.02	$67.00	$67.00
Purchase #2	$100.74	7.487%	$108.2824	$108.28	$108.30	$108.30
Purchase #3	$53.82	13.531%	$61.1024	$61.10	$61.10	$61.10
Purchase #4	$35.94	8.752%	$39.0855	$39.09	$39.10	$39.10
Purchase #5	$136.69	11.344%	$152.1961	$152.20	$152.20	$152.20
Purchase #6	$38.44	3.590%	$39.82	$39.82	$39.80	$39.80
Purchase #7	$63.78	3.389%	$65.9415	$65.94	$65.95	$65.90
7 purchase totals =	$494.36		$533.4511	$533.45	$533.45	$533.40