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	$24.29	9.462%	$26.5883	$26.59	$26.60	$26.60
Purchase #2	$233.83	9.532%	$256.1187	$256.12	$256.10	$256.10
Purchase #3	$70.65	13.860%	$80.4421	$80.44	$80.45	$80.40
Purchase #4	$49.61	3.828%	$51.5091	$51.51	$51.50	$51.50
Purchase #5	$130.36	9.199%	$142.3518	$142.35	$142.35	$142.40
Purchase #6	$178.81	9.826%	$196.3799	$196.38	$196.40	$196.40
Purchase #7	$43.29	5.249%	$45.5623	$45.56	$45.55	$45.60
7 purchase totals =	$730.84		$798.9522	$798.95	$798.95	$799.00