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	$242.82	11.821%	$271.5238	$271.52	$271.50	$271.50
Purchase #2	$212.69	8.181%	$230.0902	$230.09	$230.10	$230.10
Purchase #3	$213.32	13.458%	$242.0286	$242.03	$242.05	$242.00
Purchase #4	$47.29	12.581%	$53.2396	$53.24	$53.25	$53.20
Purchase #5	$95.51	3.800%	$99.1394	$99.14	$99.15	$99.10
Purchase #6	$138.55	10.376%	$152.9259	$152.93	$152.95	$152.90
Purchase #7	$13.67	11.217%	$15.2034	$15.20	$15.20	$15.20
7 purchase totals =	$963.85		$1,064.1509	$1,064.15	$1,064.20	$1,064.00