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	$143.38	7.624%	$154.3113	$154.31	$154.30	$154.30
Purchase #2	$54.35	9.576%	$59.5546	$59.55	$59.55	$59.60
Purchase #3	$227.90	12.200%	$255.7038	$255.70	$255.70	$255.70
Purchase #4	$205.74	8.422%	$223.0674	$223.07	$223.05	$223.10
Purchase #5	$13.41	11.660%	$14.9736	$14.97	$14.95	$15.00
Purchase #6	$67.28	13.626%	$76.4476	$76.45	$76.45	$76.40
Purchase #7	$229.39	12.510%	$258.0867	$258.09	$258.10	$258.10
7 purchase totals =	$941.45		$1,042.1450	$1,042.14	$1,042.10	$1,042.20