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	$153.39	12.340%	$172.3183	$172.32	$172.30	$172.30
Purchase #2	$153.33	13.382%	$173.8486	$173.85	$173.85	$173.80
Purchase #3	$112.52	7.871%	$121.3764	$121.38	$121.40	$121.40
Purchase #4	$82.65	8.848%	$89.9629	$89.96	$89.95	$90.00
Purchase #5	$74.85	12.613%	$84.2908	$84.29	$84.30	$84.30
Purchase #6	$86.60	7.245%	$92.8742	$92.87	$92.85	$92.90
Purchase #7	$121.77	8.299%	$131.8757	$131.88	$131.90	$131.90
7 purchase totals =	$785.11		$866.5469	$866.55	$866.55	$866.60