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	$66.42	9.461%	$72.704	$72.70	$72.70	$72.70
Purchase #2	$227.48	11.497%	$253.6334	$253.63	$253.65	$253.60
Purchase #3	$157.25	5.144%	$165.3389	$165.34	$165.35	$165.30
Purchase #4	$168.85	10.551%	$186.6654	$186.67	$186.65	$186.70
Purchase #5	$71.89	7.303%	$77.1401	$77.14	$77.15	$77.10
Purchase #6	$184.93	13.403%	$209.7162	$209.72	$209.70	$209.70
Purchase #7	$127.89	4.307%	$133.3982	$133.40	$133.40	$133.40
7 purchase totals =	$1,004.71		$1,098.5962	$1,098.60	$1,098.60	$1,098.50