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	$11.85	13.698%	$13.4732	$13.47	$13.45	$13.50
Purchase #2	$40.95	6.668%	$43.6805	$43.68	$43.70	$43.70
Purchase #3	$41.59	9.601%	$45.5831	$45.58	$45.60	$45.60
Purchase #4	$241.59	11.466%	$269.2907	$269.29	$269.30	$269.30
Purchase #5	$6.94	7.113%	$7.4336	$7.43	$7.45	$7.40
Purchase #6	$81.71	5.312%	$86.0504	$86.05	$86.05	$86.10
Purchase #7	$187.77	6.465%	$199.9093	$199.91	$199.90	$199.90
7 purchase totals =	$612.40		$665.4208	$665.41	$665.45	$665.50