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	$143.55	10.628%	$158.8065	$158.81	$158.80	$158.80
Purchase #2	$219.83	9.388%	$240.4676	$240.47	$240.45	$240.50
Purchase #3	$38.54	5.220%	$40.5518	$40.55	$40.55	$40.60
Purchase #4	$74.56	7.670%	$80.2788	$80.28	$80.30	$80.30
Purchase #5	$109.38	6.590%	$116.5881	$116.59	$116.60	$116.60
Purchase #6	$80.88	5.745%	$85.5266	$85.53	$85.55	$85.50
Purchase #7	$169.48	5.419%	$178.6641	$178.66	$178.65	$178.70
7 purchase totals =	$836.22		$900.8835	$900.89	$900.90	$901.00