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	$37.84	6.112%	$40.1528	$40.15	$40.15	$40.20
Purchase #2	$179.90	3.159%	$185.583	$185.58	$185.60	$185.60
Purchase #3	$223.72	6.758%	$238.839	$238.84	$238.85	$238.80
Purchase #4	$137.58	7.732%	$148.2177	$148.22	$148.20	$148.20
Purchase #5	$92.55	3.289%	$95.594	$95.59	$95.60	$95.60
Purchase #6	$154.28	9.131%	$168.3673	$168.37	$168.35	$168.40
Purchase #7	$246.78	13.652%	$280.4704	$280.47	$280.45	$280.50
7 purchase totals =	$1,072.65		$1,157.2242	$1,157.22	$1,157.20	$1,157.30