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	$44.83	10.453%	$49.5161	$49.52	$49.50	$49.50
Purchase #2	$13.95	4.297%	$14.5494	$14.55	$14.55	$14.50
Purchase #3	$123.72	10.467%	$136.6698	$136.67	$136.65	$136.70
Purchase #4	$79.61	4.625%	$83.292	$83.29	$83.30	$83.30
Purchase #5	$133.87	13.745%	$152.2704	$152.27	$152.25	$152.30
Purchase #6	$126.93	11.227%	$141.1804	$141.18	$141.20	$141.20
Purchase #7	$127.32	12.598%	$143.3598	$143.36	$143.35	$143.40
7 purchase totals =	$650.23		$720.8379	$720.84	$720.80	$720.90