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	$42.66	13.806%	$48.5496	$48.55	$48.55	$48.50
Purchase #2	$233.75	7.517%	$251.321	$251.32	$251.30	$251.30
Purchase #3	$36.39	5.221%	$38.2899	$38.29	$38.30	$38.30
Purchase #4	$175.90	10.628%	$194.5947	$194.59	$194.60	$194.60
Purchase #5	$104.47	4.695%	$109.3749	$109.37	$109.35	$109.40
Purchase #6	$55.57	12.344%	$62.4296	$62.43	$62.45	$62.40
Purchase #7	$95.77	13.797%	$108.9834	$108.98	$109.00	$109.00
7 purchase totals =	$744.51		$813.5431	$813.53	$813.55	$813.50