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	$236.42	6.845%	$252.6029	$252.60	$252.60	$252.60
Purchase #2	$37.94	5.430%	$40.0001	$40.00	$40.00	$40.00
Purchase #3	$86.35	3.791%	$89.6235	$89.62	$89.60	$89.60
Purchase #4	$100.95	10.321%	$111.369	$111.37	$111.35	$111.40
Purchase #5	$129.59	3.507%	$134.1347	$134.13	$134.15	$134.10
Purchase #6	$65.55	10.690%	$72.5573	$72.56	$72.55	$72.60
Purchase #7	$23.80	10.631%	$26.3302	$26.33	$26.35	$26.30
7 purchase totals =	$680.60		$726.6177	$726.61	$726.60	$726.60