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	$26.29	8.313%	$28.4755	$28.48	$28.50	$28.50
Purchase #2	$45.67	5.159%	$48.0261	$48.03	$48.05	$48.00
Purchase #3	$239.84	11.520%	$267.4696	$267.47	$267.45	$267.50
Purchase #4	$66.80	9.111%	$72.8861	$72.89	$72.90	$72.90
Purchase #5	$124.35	11.685%	$138.8803	$138.88	$138.90	$138.90
Purchase #6	$163.47	4.238%	$170.3979	$170.40	$170.40	$170.40
Purchase #7	$99.39	12.535%	$111.8485	$111.85	$111.85	$111.80
7 purchase totals =	$765.81		$837.9840	$838.00	$838.05	$838.00