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	$11.45	10.213%	$12.6194	$12.62	$12.60	$12.60
Purchase #2	$54.98	4.775%	$57.6053	$57.61	$57.60	$57.60
Purchase #3	$202.37	9.873%	$222.35	$222.35	$222.35	$222.40
Purchase #4	$46.86	11.444%	$52.2227	$52.22	$52.20	$52.20
Purchase #5	$168.98	9.679%	$185.3356	$185.34	$185.35	$185.30
Purchase #6	$243.25	7.612%	$261.7662	$261.77	$261.75	$261.80
Purchase #7	$44.83	3.446%	$46.3748	$46.37	$46.35	$46.40
7 purchase totals =	$772.72		$838.2740	$838.28	$838.20	$838.30