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	$135.49	5.502%	$142.9447	$142.94	$142.95	$142.90
Purchase #2	$214.41	12.207%	$240.583	$240.58	$240.60	$240.60
Purchase #3	$63.90	5.417%	$67.3615	$67.36	$67.35	$67.40
Purchase #4	$190.99	10.192%	$210.4557	$210.46	$210.45	$210.50
Purchase #5	$18.90	5.388%	$19.9183	$19.92	$19.90	$19.90
Purchase #6	$136.71	5.615%	$144.3863	$144.39	$144.40	$144.40
Purchase #7	$78.85	5.199%	$82.9494	$82.95	$82.95	$82.90
7 purchase totals =	$839.25		$908.5989	$908.60	$908.60	$908.60