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	$72.98	10.290%	$80.4896	$80.49	$80.50	$80.50
Purchase #2	$127.55	11.268%	$141.9223	$141.92	$141.90	$141.90
Purchase #3	$66.81	12.858%	$75.4004	$75.40	$75.40	$75.40
Purchase #4	$83.79	8.138%	$90.6088	$90.61	$90.60	$90.60
Purchase #5	$187.82	4.393%	$196.0709	$196.07	$196.05	$196.10
Purchase #6	$139.51	12.147%	$156.4563	$156.46	$156.45	$156.50
Purchase #7	$79.31	5.575%	$83.7315	$83.73	$83.75	$83.70
7 purchase totals =	$757.77		$824.6798	$824.68	$824.65	$824.70