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	$62.37	8.736%	$67.8186	$67.82	$67.80	$67.80
Purchase #2	$230.73	12.119%	$258.6922	$258.69	$258.70	$258.70
Purchase #3	$136.39	12.813%	$153.8657	$153.87	$153.85	$153.90
Purchase #4	$78.30	9.823%	$85.9914	$85.99	$86.00	$86.00
Purchase #5	$47.72	8.234%	$51.6493	$51.65	$51.65	$51.60
Purchase #6	$211.71	13.557%	$240.4115	$240.41	$240.40	$240.40
Purchase #7	$92.35	12.178%	$103.5964	$103.60	$103.60	$103.60
7 purchase totals =	$859.57		$962.0251	$962.03	$962.00	$962.00