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	$52.61	13.171%	$59.5393	$59.54	$59.55	$59.50
Purchase #2	$160.40	5.420%	$169.0937	$169.09	$169.10	$169.10
Purchase #3	$235.78	13.171%	$266.8346	$266.83	$266.85	$266.80
Purchase #4	$224.42	7.134%	$240.4301	$240.43	$240.45	$240.40
Purchase #5	$246.55	13.694%	$280.3126	$280.31	$280.30	$280.30
Purchase #6	$225.54	7.578%	$242.6314	$242.63	$242.65	$242.60
Purchase #7	$94.60	10.624%	$104.6503	$104.65	$104.65	$104.70
7 purchase totals =	$1,239.90		$1,363.4920	$1,363.48	$1,363.55	$1,363.40