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	$12.49	10.686%	$13.8247	$13.82	$13.80	$13.80
Purchase #2	$168.86	12.263%	$189.5673	$189.57	$189.55	$189.60
Purchase #3	$230.29	11.135%	$255.9328	$255.93	$255.95	$255.90
Purchase #4	$42.56	11.820%	$47.5906	$47.59	$47.60	$47.60
Purchase #5	$84.49	3.608%	$87.5384	$87.54	$87.55	$87.50
Purchase #6	$205.47	12.271%	$230.6832	$230.68	$230.70	$230.70
Purchase #7	$47.95	13.575%	$54.4592	$54.46	$54.45	$54.50
7 purchase totals =	$792.11		$879.5962	$879.59	$879.60	$879.60