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	$12.60	10.267%	$13.8936	$13.89	$13.90	$13.90
Purchase #2	$34.84	9.728%	$38.2292	$38.23	$38.25	$38.20
Purchase #3	$83.40	5.338%	$87.8519	$87.85	$87.85	$87.90
Purchase #4	$34.89	12.703%	$39.3221	$39.32	$39.30	$39.30
Purchase #5	$250.33	13.243%	$283.4812	$283.48	$283.50	$283.50
Purchase #6	$98.56	11.105%	$109.5051	$109.51	$109.50	$109.50
Purchase #7	$240.44	6.803%	$256.7971	$256.80	$256.80	$256.80
7 purchase totals =	$755.06		$829.0802	$829.08	$829.10	$829.10