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	$155.25	3.407%	$160.5394	$160.54	$160.55	$160.50
Purchase #2	$169.85	9.421%	$185.8516	$185.85	$185.85	$185.90
Purchase #3	$153.79	13.792%	$175.0007	$175.00	$175.00	$175.00
Purchase #4	$236.79	8.105%	$255.9818	$255.98	$256.00	$256.00
Purchase #5	$53.37	11.601%	$59.5615	$59.56	$59.55	$59.60
Purchase #6	$194.83	10.550%	$215.3846	$215.38	$215.40	$215.40
Purchase #7	$179.64	13.556%	$203.992	$203.99	$204.00	$204.00
7 purchase totals =	$1,143.52		$1,256.3116	$1,256.30	$1,256.35	$1,256.40