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	$88.49	5.665%	$93.503	$93.50	$93.50	$93.50
Purchase #2	$244.26	13.314%	$276.7808	$276.78	$276.80	$276.80
Purchase #3	$151.25	11.281%	$168.3125	$168.31	$168.30	$168.30
Purchase #4	$35.58	4.607%	$37.2192	$37.22	$37.20	$37.20
Purchase #5	$238.60	3.357%	$246.6098	$246.61	$246.60	$246.60
Purchase #6	$88.93	12.848%	$100.3557	$100.36	$100.35	$100.40
Purchase #7	$52.42	5.518%	$55.3125	$55.31	$55.30	$55.30
7 purchase totals =	$899.53		$978.0935	$978.09	$978.05	$978.10