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	$52.90	6.312%	$56.239	$56.24	$56.25	$56.20
Purchase #2	$77.39	7.734%	$83.3753	$83.38	$83.40	$83.40
Purchase #3	$171.27	8.486%	$185.804	$185.80	$185.80	$185.80
Purchase #4	$233.26	3.550%	$241.5407	$241.54	$241.55	$241.50
Purchase #5	$16.31	13.117%	$18.4494	$18.45	$18.45	$18.40
Purchase #6	$243.43	12.643%	$274.2069	$274.21	$274.20	$274.20
Purchase #7	$104.48	6.460%	$111.2294	$111.23	$111.25	$111.20
7 purchase totals =	$899.04		$970.8447	$970.85	$970.90	$970.70