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	$37.35	4.206%	$38.9209	$38.92	$38.90	$38.90
Purchase #2	$56.45	9.389%	$61.7501	$61.75	$61.75	$61.80
Purchase #3	$49.54	11.350%	$55.1628	$55.16	$55.15	$55.20
Purchase #4	$58.59	10.826%	$64.933	$64.93	$64.95	$64.90
Purchase #5	$86.37	3.571%	$89.4543	$89.45	$89.45	$89.50
Purchase #6	$29.62	6.678%	$31.598	$31.60	$31.60	$31.60
Purchase #7	$199.50	9.168%	$217.7902	$217.79	$217.80	$217.80
7 purchase totals =	$517.42		$559.6093	$559.60	$559.60	$559.70