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	$105.75	7.369%	$113.5427	$113.54	$113.55	$113.50
Purchase #2	$34.57	12.831%	$39.0057	$39.01	$39.00	$39.00
Purchase #3	$138.43	5.744%	$146.3814	$146.38	$146.40	$146.40
Purchase #4	$27.66	11.530%	$30.8492	$30.85	$30.85	$30.80
Purchase #5	$7.58	5.679%	$8.0105	$8.01	$8.00	$8.00
Purchase #6	$176.96	11.215%	$196.8061	$196.81	$196.80	$196.80
Purchase #7	$43.92	3.766%	$45.574	$45.57	$45.55	$45.60
7 purchase totals =	$534.87		$580.1696	$580.17	$580.15	$580.10