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	$158.28	13.726%	$180.0055	$180.01	$180.00	$180.00
Purchase #2	$56.68	4.306%	$59.1206	$59.12	$59.10	$59.10
Purchase #3	$73.60	9.674%	$80.7201	$80.72	$80.70	$80.70
Purchase #4	$39.90	13.605%	$45.3284	$45.33	$45.35	$45.30
Purchase #5	$12.43	11.228%	$13.8256	$13.83	$13.85	$13.80
Purchase #6	$12.33	4.838%	$12.9265	$12.93	$12.95	$12.90
Purchase #7	$115.43	12.594%	$129.9673	$129.97	$129.95	$130.00
7 purchase totals =	$468.65		$521.8940	$521.91	$521.90	$521.80