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	$125.87	5.241%	$132.4668	$132.47	$132.45	$132.50
Purchase #2	$205.96	12.546%	$231.7997	$231.80	$231.80	$231.80
Purchase #3	$243.39	9.647%	$266.8698	$266.87	$266.85	$266.90
Purchase #4	$102.59	6.757%	$109.522	$109.52	$109.50	$109.50
Purchase #5	$180.33	6.623%	$192.2733	$192.27	$192.25	$192.30
Purchase #6	$114.37	5.664%	$120.8479	$120.85	$120.85	$120.80
Purchase #7	$31.88	12.235%	$35.7805	$35.78	$35.80	$35.80
7 purchase totals =	$1,004.39		$1,089.5600	$1,089.56	$1,089.50	$1,089.60