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	$28.54	10.205%	$31.4525	$31.45	$31.45	$31.50
Purchase #2	$198.60	3.604%	$205.7575	$205.76	$205.75	$205.80
Purchase #3	$168.35	3.238%	$173.8012	$173.80	$173.80	$173.80
Purchase #4	$88.93	12.655%	$100.1841	$100.18	$100.20	$100.20
Purchase #5	$161.25	10.573%	$178.299	$178.30	$178.30	$178.30
Purchase #6	$132.27	13.647%	$150.3209	$150.32	$150.30	$150.30
Purchase #7	$11.83	12.469%	$13.3051	$13.31	$13.30	$13.30
7 purchase totals =	$789.77		$853.1203	$853.12	$853.10	$853.20