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	$229.68	11.771%	$256.7156	$256.72	$256.70	$256.70
Purchase #2	$56.75	5.237%	$59.722	$59.72	$59.70	$59.70
Purchase #3	$158.70	3.661%	$164.51	$164.51	$164.50	$164.50
Purchase #4	$164.37	4.171%	$171.2259	$171.23	$171.25	$171.20
Purchase #5	$95.83	13.408%	$108.6789	$108.68	$108.70	$108.70
Purchase #6	$99.89	6.493%	$106.3759	$106.38	$106.40	$106.40
Purchase #7	$38.61	11.550%	$43.0695	$43.07	$43.05	$43.10
7 purchase totals =	$843.83		$910.2978	$910.31	$910.30	$910.30