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	$52.66	8.718%	$57.2509	$57.25	$57.25	$57.30
Purchase #2	$11.64	10.680%	$12.8832	$12.88	$12.90	$12.90
Purchase #3	$173.95	9.825%	$191.0406	$191.04	$191.05	$191.00
Purchase #4	$226.49	8.674%	$246.1357	$246.14	$246.15	$246.10
Purchase #5	$81.85	5.732%	$86.5416	$86.54	$86.55	$86.50
Purchase #6	$59.27	11.177%	$65.8946	$65.89	$65.90	$65.90
Purchase #7	$107.60	3.862%	$111.7555	$111.76	$111.75	$111.80
7 purchase totals =	$713.46		$771.5021	$771.50	$771.55	$771.50