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	$245.87	12.411%	$276.3849	$276.38	$276.40	$276.40
Purchase #2	$104.49	4.150%	$108.8263	$108.83	$108.85	$108.80
Purchase #3	$66.73	9.262%	$72.9105	$72.91	$72.90	$72.90
Purchase #4	$108.89	10.680%	$120.5195	$120.52	$120.50	$120.50
Purchase #5	$81.40	10.395%	$89.8615	$89.86	$89.85	$89.90
Purchase #6	$58.77	6.127%	$62.3708	$62.37	$62.35	$62.40
Purchase #7	$135.43	5.332%	$142.6511	$142.65	$142.65	$142.70
7 purchase totals =	$801.58		$873.5246	$873.52	$873.50	$873.60