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	$52.42	13.263%	$59.3725	$59.37	$59.35	$59.40
Purchase #2	$116.34	11.726%	$129.982	$129.98	$130.00	$130.00
Purchase #3	$24.52	6.569%	$26.1307	$26.13	$26.15	$26.10
Purchase #4	$138.28	10.452%	$152.733	$152.73	$152.75	$152.70
Purchase #5	$125.98	12.723%	$142.0084	$142.01	$142.00	$142.00
Purchase #6	$198.45	10.109%	$218.5113	$218.51	$218.50	$218.50
Purchase #7	$102.29	9.271%	$111.7733	$111.77	$111.75	$111.80
7 purchase totals =	$758.28		$840.5112	$840.50	$840.50	$840.50