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	$81.72	10.836%	$90.5752	$90.58	$90.60	$90.60
Purchase #2	$234.51	3.366%	$242.4036	$242.40	$242.40	$242.40
Purchase #3	$153.97	6.540%	$164.0396	$164.04	$164.05	$164.00
Purchase #4	$211.65	3.460%	$218.9731	$218.97	$218.95	$219.00
Purchase #5	$215.48	11.406%	$240.0576	$240.06	$240.05	$240.10
Purchase #6	$134.27	5.672%	$141.8858	$141.89	$141.90	$141.90
Purchase #7	$192.62	3.466%	$199.2962	$199.30	$199.30	$199.30
7 purchase totals =	$1,224.22		$1,297.2311	$1,297.24	$1,297.25	$1,297.30