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	$32.68	12.338%	$36.7121	$36.71	$36.70	$36.70
Purchase #2	$30.41	9.278%	$33.2314	$33.23	$33.25	$33.20
Purchase #3	$184.88	8.637%	$200.8481	$200.85	$200.85	$200.80
Purchase #4	$20.98	12.856%	$23.6772	$23.68	$23.70	$23.70
Purchase #5	$138.81	4.360%	$144.8621	$144.86	$144.85	$144.90
Purchase #6	$82.45	8.653%	$89.5844	$89.58	$89.60	$89.60
Purchase #7	$113.36	4.490%	$118.4499	$118.45	$118.45	$118.40
7 purchase totals =	$603.57		$647.3652	$647.36	$647.40	$647.30