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	$36.77	4.493%	$38.4221	$38.42	$38.40	$38.40
Purchase #2	$181.89	7.110%	$194.8224	$194.82	$194.80	$194.80
Purchase #3	$88.81	12.196%	$99.6413	$99.64	$99.65	$99.60
Purchase #4	$57.62	5.506%	$60.7926	$60.79	$60.80	$60.80
Purchase #5	$178.72	5.289%	$188.1725	$188.17	$188.15	$188.20
Purchase #6	$163.25	9.621%	$178.9563	$178.96	$178.95	$179.00
Purchase #7	$225.52	6.625%	$240.4607	$240.46	$240.45	$240.50
7 purchase totals =	$932.58		$1,001.2679	$1,001.26	$1,001.20	$1,001.30