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	$127.86	12.146%	$143.3899	$143.39	$143.40	$143.40
Purchase #2	$16.96	9.488%	$18.5692	$18.57	$18.55	$18.60
Purchase #3	$144.35	12.541%	$162.4529	$162.45	$162.45	$162.50
Purchase #4	$49.55	7.798%	$53.4139	$53.41	$53.40	$53.40
Purchase #5	$136.93	5.470%	$144.4201	$144.42	$144.40	$144.40
Purchase #6	$203.84	7.597%	$219.3257	$219.33	$219.35	$219.30
Purchase #7	$42.37	9.433%	$46.3668	$46.37	$46.35	$46.40
7 purchase totals =	$721.86		$787.9385	$787.94	$787.90	$788.00