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	$108.30	7.536%	$116.4615	$116.46	$116.45	$116.50
Purchase #2	$163.48	11.278%	$181.9173	$181.92	$181.90	$181.90
Purchase #3	$104.58	7.304%	$112.2185	$112.22	$112.20	$112.20
Purchase #4	$78.55	5.355%	$82.7564	$82.76	$82.75	$82.80
Purchase #5	$126.31	12.397%	$141.9687	$141.97	$141.95	$142.00
Purchase #6	$53.39	11.621%	$59.5945	$59.59	$59.60	$59.60
Purchase #7	$192.80	8.313%	$208.8275	$208.83	$208.85	$208.80
7 purchase totals =	$827.41		$903.7444	$903.75	$903.70	$903.80