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	$109.66	8.834%	$119.3474	$119.35	$119.35	$119.30
Purchase #2	$78.73	13.806%	$89.5995	$89.60	$89.60	$89.60
Purchase #3	$39.88	10.355%	$44.0096	$44.01	$44.00	$44.00
Purchase #4	$201.35	11.202%	$223.9052	$223.91	$223.90	$223.90
Purchase #5	$12.95	7.408%	$13.9093	$13.91	$13.90	$13.90
Purchase #6	$49.52	3.259%	$51.1339	$51.13	$51.15	$51.10
Purchase #7	$58.60	13.393%	$66.4483	$66.45	$66.45	$66.40
7 purchase totals =	$550.69		$608.3532	$608.36	$608.35	$608.20