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	$38.64	4.528%	$40.3896	$40.39	$40.40	$40.40
Purchase #2	$146.86	11.309%	$163.4684	$163.47	$163.45	$163.50
Purchase #3	$72.30	13.237%	$81.8704	$81.87	$81.85	$81.90
Purchase #4	$229.34	9.315%	$250.703	$250.70	$250.70	$250.70
Purchase #5	$41.28	3.711%	$42.8119	$42.81	$42.80	$42.80
Purchase #6	$42.48	9.292%	$46.4272	$46.43	$46.45	$46.40
Purchase #7	$223.46	6.873%	$238.8184	$238.82	$238.80	$238.80
7 purchase totals =	$794.36		$864.4889	$864.49	$864.45	$864.50