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	$116.47	12.827%	$131.4096	$131.41	$131.40	$131.40
Purchase #2	$66.83	9.149%	$72.9443	$72.94	$72.95	$72.90
Purchase #3	$67.47	4.852%	$70.7436	$70.74	$70.75	$70.70
Purchase #4	$144.44	12.240%	$162.1195	$162.12	$162.10	$162.10
Purchase #5	$230.52	12.777%	$259.9735	$259.97	$259.95	$260.00
Purchase #6	$100.78	12.688%	$113.567	$113.57	$113.55	$113.60
Purchase #7	$174.32	8.804%	$189.6671	$189.67	$189.65	$189.70
7 purchase totals =	$900.83		$1,000.4246	$1,000.42	$1,000.35	$1,000.40