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	$82.44	8.836%	$89.7244	$89.72	$89.70	$89.70
Purchase #2	$108.92	6.460%	$115.9562	$115.96	$115.95	$116.00
Purchase #3	$24.47	13.166%	$27.6917	$27.69	$27.70	$27.70
Purchase #4	$30.90	4.692%	$32.3498	$32.35	$32.35	$32.30
Purchase #5	$231.56	13.153%	$262.0171	$262.02	$262.00	$262.00
Purchase #6	$108.64	9.488%	$118.9478	$118.95	$118.95	$118.90
Purchase #7	$240.42	12.134%	$269.5926	$269.59	$269.60	$269.60
7 purchase totals =	$827.35		$916.2796	$916.28	$916.25	$916.20