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	$248.95	5.738%	$263.2348	$263.23	$263.25	$263.20
Purchase #2	$139.40	10.510%	$154.0509	$154.05	$154.05	$154.10
Purchase #3	$34.49	7.373%	$37.0329	$37.03	$37.05	$37.00
Purchase #4	$40.69	3.520%	$42.1223	$42.12	$42.10	$42.10
Purchase #5	$155.41	7.149%	$166.5203	$166.52	$166.50	$166.50
Purchase #6	$227.59	12.479%	$255.991	$255.99	$256.00	$256.00
Purchase #7	$20.35	10.653%	$22.5179	$22.52	$22.50	$22.50
7 purchase totals =	$866.88		$941.4701	$941.46	$941.45	$941.40