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	$81.25	11.349%	$90.4711	$90.47	$90.45	$90.50
Purchase #2	$80.88	3.304%	$83.5523	$83.55	$83.55	$83.60
Purchase #3	$160.84	10.743%	$178.119	$178.12	$178.10	$178.10
Purchase #4	$53.32	10.712%	$59.0316	$59.03	$59.05	$59.00
Purchase #5	$229.25	8.472%	$248.6721	$248.67	$248.65	$248.70
Purchase #6	$15.32	13.255%	$17.3507	$17.35	$17.35	$17.40
Purchase #7	$194.58	5.739%	$205.7469	$205.75	$205.75	$205.70
7 purchase totals =	$815.44		$882.9437	$882.94	$882.90	$883.00