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	$250.80	10.244%	$276.492	$276.49	$276.50	$276.50
Purchase #2	$11.80	13.368%	$13.3774	$13.38	$13.40	$13.40
Purchase #3	$60.79	8.510%	$65.9632	$65.96	$65.95	$66.00
Purchase #4	$42.43	7.478%	$45.6029	$45.60	$45.60	$45.60
Purchase #5	$46.37	8.409%	$50.2693	$50.27	$50.25	$50.30
Purchase #6	$73.90	6.340%	$78.5853	$78.59	$78.60	$78.60
Purchase #7	$24.28	5.612%	$25.6426	$25.64	$25.65	$25.60
7 purchase totals =	$510.37		$555.9327	$555.93	$555.95	$556.00