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	$90.40	13.724%	$102.8065	$102.81	$102.80	$102.80
Purchase #2	$242.31	10.352%	$267.3939	$267.39	$267.40	$267.40
Purchase #3	$196.39	12.691%	$221.3139	$221.31	$221.30	$221.30
Purchase #4	$223.45	12.288%	$250.9075	$250.91	$250.90	$250.90
Purchase #5	$100.54	7.536%	$108.1167	$108.12	$108.10	$108.10
Purchase #6	$66.31	9.249%	$72.443	$72.44	$72.45	$72.40
Purchase #7	$141.72	8.846%	$154.2566	$154.26	$154.25	$154.30
7 purchase totals =	$1,061.12		$1,177.2381	$1,177.24	$1,177.20	$1,177.20