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	$90.59	9.722%	$99.3972	$99.40	$99.40	$99.40
Purchase #2	$91.54	8.298%	$99.136	$99.14	$99.15	$99.10
Purchase #3	$129.25	9.488%	$141.5132	$141.51	$141.50	$141.50
Purchase #4	$142.27	5.794%	$150.5131	$150.51	$150.50	$150.50
Purchase #5	$153.70	5.124%	$161.5756	$161.58	$161.60	$161.60
Purchase #6	$99.60	13.830%	$113.3747	$113.37	$113.35	$113.40
Purchase #7	$40.94	12.821%	$46.1889	$46.19	$46.20	$46.20
7 purchase totals =	$747.89		$811.6987	$811.70	$811.70	$811.70