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	$245.40	4.724%	$256.9927	$256.99	$257.00	$257.00
Purchase #2	$174.88	10.836%	$193.83	$193.83	$193.85	$193.80
Purchase #3	$231.30	4.147%	$240.892	$240.89	$240.90	$240.90
Purchase #4	$82.62	8.448%	$89.5997	$89.60	$89.60	$89.60
Purchase #5	$86.34	4.771%	$90.4593	$90.46	$90.45	$90.50
Purchase #6	$226.28	10.341%	$249.6796	$249.68	$249.70	$249.70
Purchase #7	$30.59	7.710%	$32.9485	$32.95	$32.95	$32.90
7 purchase totals =	$1,077.41		$1,154.4018	$1,154.40	$1,154.45	$1,154.40