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	$245.96	9.292%	$268.8146	$268.81	$268.80	$268.80
Purchase #2	$16.94	8.718%	$18.4168	$18.42	$18.40	$18.40
Purchase #3	$177.74	12.872%	$200.6187	$200.62	$200.60	$200.60
Purchase #4	$71.50	11.683%	$79.8533	$79.85	$79.85	$79.90
Purchase #5	$151.78	4.367%	$158.4082	$158.41	$158.40	$158.40
Purchase #6	$132.31	10.587%	$146.3177	$146.32	$146.30	$146.30
Purchase #7	$12.50	5.103%	$13.1379	$13.14	$13.15	$13.10
7 purchase totals =	$808.73		$885.5672	$885.57	$885.50	$885.50