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	$40.53	10.611%	$44.8306	$44.83	$44.85	$44.80
Purchase #2	$36.90	7.325%	$39.6029	$39.60	$39.60	$39.60
Purchase #3	$124.78	12.840%	$140.8018	$140.80	$140.80	$140.80
Purchase #4	$173.86	6.421%	$185.0236	$185.02	$185.00	$185.00
Purchase #5	$241.25	11.417%	$268.7935	$268.79	$268.80	$268.80
Purchase #6	$61.38	6.270%	$65.2285	$65.23	$65.25	$65.20
Purchase #7	$151.61	4.323%	$158.1641	$158.16	$158.15	$158.20
7 purchase totals =	$830.31		$902.4450	$902.43	$902.45	$902.40