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	$39.50	8.561%	$42.8816	$42.88	$42.90	$42.90
Purchase #2	$120.83	5.756%	$127.785	$127.79	$127.80	$127.80
Purchase #3	$42.96	8.678%	$46.6881	$46.69	$46.70	$46.70
Purchase #4	$89.75	11.592%	$100.1538	$100.15	$100.15	$100.20
Purchase #5	$68.59	6.787%	$73.2452	$73.25	$73.25	$73.20
Purchase #6	$33.84	11.380%	$37.691	$37.69	$37.70	$37.70
Purchase #7	$17.55	13.577%	$19.9328	$19.93	$19.95	$19.90
7 purchase totals =	$413.02		$448.3775	$448.38	$448.45	$448.40