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	$99.60	12.354%	$111.9046	$111.90	$111.90	$111.90
Purchase #2	$223.69	11.401%	$249.1929	$249.19	$249.20	$249.20
Purchase #3	$55.25	10.208%	$60.8899	$60.89	$60.90	$60.90
Purchase #4	$65.36	11.361%	$72.7855	$72.79	$72.80	$72.80
Purchase #5	$228.62	5.466%	$241.1164	$241.12	$241.10	$241.10
Purchase #6	$195.82	12.303%	$219.9117	$219.91	$219.90	$219.90
Purchase #7	$110.91	10.697%	$122.774	$122.77	$122.75	$122.80
7 purchase totals =	$979.25		$1,078.5750	$1,078.57	$1,078.55	$1,078.60