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	$78.47	13.171%	$88.8053	$88.81	$88.80	$88.80
Purchase #2	$47.34	12.830%	$53.4137	$53.41	$53.40	$53.40
Purchase #3	$50.35	7.701%	$54.2275	$54.23	$54.25	$54.20
Purchase #4	$151.40	3.743%	$157.0669	$157.07	$157.05	$157.10
Purchase #5	$168.52	10.271%	$185.8287	$185.83	$185.85	$185.80
Purchase #6	$118.40	8.856%	$128.8855	$128.89	$128.90	$128.90
Purchase #7	$15.79	6.304%	$16.7854	$16.79	$16.80	$16.80
7 purchase totals =	$630.27		$685.0130	$685.03	$685.05	$685.00