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	$31.59	10.203%	$34.8131	$34.81	$34.80	$34.80
Purchase #2	$94.73	5.133%	$99.5925	$99.59	$99.60	$99.60
Purchase #3	$225.83	6.525%	$240.5654	$240.57	$240.55	$240.60
Purchase #4	$193.68	8.470%	$210.0847	$210.08	$210.10	$210.10
Purchase #5	$245.65	6.442%	$261.4748	$261.47	$261.45	$261.50
Purchase #6	$45.52	6.204%	$48.3441	$48.34	$48.35	$48.30
Purchase #7	$82.89	7.282%	$88.926	$88.93	$88.95	$88.90
7 purchase totals =	$919.89		$983.8006	$983.79	$983.80	$983.80