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	$79.63	3.724%	$82.5954	$82.60	$82.60	$82.60
Purchase #2	$88.36	12.825%	$99.6922	$99.69	$99.70	$99.70
Purchase #3	$66.74	11.483%	$74.4038	$74.40	$74.40	$74.40
Purchase #4	$97.54	6.730%	$104.1044	$104.10	$104.10	$104.10
Purchase #5	$201.82	6.656%	$215.2531	$215.25	$215.25	$215.30
Purchase #6	$102.49	8.725%	$111.4323	$111.43	$111.45	$111.40
Purchase #7	$100.74	12.183%	$113.0132	$113.01	$113.00	$113.00
7 purchase totals =	$737.32		$800.4944	$800.48	$800.50	$800.50