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	$146.71	13.251%	$166.1505	$166.15	$166.15	$166.20
Purchase #2	$150.56	10.658%	$166.6067	$166.61	$166.60	$166.60
Purchase #3	$99.75	13.856%	$113.5714	$113.57	$113.55	$113.60
Purchase #4	$155.94	3.307%	$161.0969	$161.10	$161.10	$161.10
Purchase #5	$36.58	5.542%	$38.6073	$38.61	$38.60	$38.60
Purchase #6	$248.32	12.194%	$278.6001	$278.60	$278.60	$278.60
Purchase #7	$28.32	11.807%	$31.6637	$31.66	$31.65	$31.70
7 purchase totals =	$866.18		$956.2966	$956.30	$956.25	$956.40