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	$67.88	8.345%	$73.5446	$73.54	$73.55	$73.50
Purchase #2	$146.95	5.844%	$155.5378	$155.54	$155.55	$155.50
Purchase #3	$156.90	7.461%	$168.6063	$168.61	$168.60	$168.60
Purchase #4	$36.36	5.307%	$38.2896	$38.29	$38.30	$38.30
Purchase #5	$81.82	12.495%	$92.0434	$92.04	$92.05	$92.00
Purchase #6	$126.96	3.682%	$131.6347	$131.63	$131.65	$131.60
Purchase #7	$23.36	10.308%	$25.7679	$25.77	$25.75	$25.80
7 purchase totals =	$640.23		$685.4243	$685.42	$685.45	$685.30