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	$40.75	4.344%	$42.5202	$42.52	$42.50	$42.50
Purchase #2	$94.88	13.179%	$107.3842	$107.38	$107.40	$107.40
Purchase #3	$91.63	13.292%	$103.8095	$103.81	$103.80	$103.80
Purchase #4	$52.83	5.440%	$55.704	$55.70	$55.70	$55.70
Purchase #5	$119.43	3.177%	$123.2243	$123.22	$123.20	$123.20
Purchase #6	$38.96	7.506%	$41.8843	$41.88	$41.90	$41.90
Purchase #7	$11.48	11.842%	$12.8395	$12.84	$12.85	$12.80
7 purchase totals =	$449.96		$487.3660	$487.35	$487.35	$487.30