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	$21.47	4.733%	$22.4862	$22.49	$22.50	$22.50
Purchase #2	$239.98	6.608%	$255.8379	$255.84	$255.85	$255.80
Purchase #3	$225.57	8.818%	$245.4608	$245.46	$245.45	$245.50
Purchase #4	$86.32	5.346%	$90.9347	$90.93	$90.95	$90.90
Purchase #5	$5.38	11.646%	$6.0066	$6.01	$6.00	$6.00
Purchase #6	$38.35	6.171%	$40.7166	$40.72	$40.70	$40.70
Purchase #7	$22.78	13.615%	$25.8815	$25.88	$25.90	$25.90
7 purchase totals =	$639.85		$687.3243	$687.33	$687.35	$687.30