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	$128.99	5.750%	$136.4069	$136.41	$136.40	$136.40
Purchase #2	$173.76	7.221%	$186.3072	$186.31	$186.30	$186.30
Purchase #3	$115.84	6.460%	$123.3233	$123.32	$123.30	$123.30
Purchase #4	$44.41	7.419%	$47.7048	$47.70	$47.70	$47.70
Purchase #5	$156.38	10.566%	$172.9031	$172.90	$172.90	$172.90
Purchase #6	$54.80	8.522%	$59.4701	$59.47	$59.45	$59.50
Purchase #7	$29.45	3.133%	$30.3727	$30.37	$30.35	$30.40
7 purchase totals =	$703.63		$756.4881	$756.48	$756.40	$756.50