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	$123.95	3.771%	$128.6242	$128.62	$128.60	$128.60
Purchase #2	$232.57	4.150%	$242.2217	$242.22	$242.20	$242.20
Purchase #3	$101.80	9.603%	$111.5759	$111.58	$111.60	$111.60
Purchase #4	$148.52	9.438%	$162.5373	$162.54	$162.55	$162.50
Purchase #5	$137.81	10.317%	$152.0279	$152.03	$152.05	$152.00
Purchase #6	$32.97	13.272%	$37.3458	$37.35	$37.35	$37.30
Purchase #7	$51.88	10.524%	$57.3399	$57.34	$57.35	$57.30
7 purchase totals =	$829.50		$891.6727	$891.68	$891.70	$891.50