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	$243.42	12.189%	$273.0905	$273.09	$273.10	$273.10
Purchase #2	$55.27	13.831%	$62.9144	$62.91	$62.90	$62.90
Purchase #3	$203.40	9.212%	$222.1372	$222.14	$222.15	$222.10
Purchase #4	$87.54	13.813%	$99.6319	$99.63	$99.65	$99.60
Purchase #5	$12.84	3.552%	$13.2961	$13.30	$13.30	$13.30
Purchase #6	$133.45	7.446%	$143.3867	$143.39	$143.40	$143.40
Purchase #7	$21.28	6.103%	$22.5787	$22.58	$22.60	$22.60
7 purchase totals =	$757.20		$837.0355	$837.04	$837.10	$837.00