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	$30.91	9.734%	$33.9188	$33.92	$33.90	$33.90
Purchase #2	$59.47	13.656%	$67.5912	$67.59	$67.60	$67.60
Purchase #3	$53.87	10.251%	$59.3922	$59.39	$59.40	$59.40
Purchase #4	$141.79	8.874%	$154.3724	$154.37	$154.35	$154.40
Purchase #5	$76.64	3.432%	$79.2703	$79.27	$79.25	$79.30
Purchase #6	$145.71	4.571%	$152.3704	$152.37	$152.35	$152.40
Purchase #7	$195.68	9.639%	$214.5416	$214.54	$214.55	$214.50
7 purchase totals =	$704.07		$761.4569	$761.45	$761.40	$761.50