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	$80.60	12.558%	$90.7217	$90.72	$90.70	$90.70
Purchase #2	$232.37	13.569%	$263.9003	$263.90	$263.90	$263.90
Purchase #3	$172.58	7.401%	$185.3526	$185.35	$185.35	$185.40
Purchase #4	$101.81	9.869%	$111.8576	$111.86	$111.85	$111.90
Purchase #5	$186.97	3.872%	$194.2095	$194.21	$194.20	$194.20
Purchase #6	$108.37	10.770%	$120.0414	$120.04	$120.05	$120.00
Purchase #7	$108.80	4.104%	$113.2652	$113.27	$113.25	$113.30
7 purchase totals =	$991.50		$1,079.3483	$1,079.35	$1,079.30	$1,079.40