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	$46.30	13.595%	$52.5945	$52.59	$52.60	$52.60
Purchase #2	$125.72	5.409%	$132.5202	$132.52	$132.50	$132.50
Purchase #3	$193.46	12.498%	$217.6386	$217.64	$217.65	$217.60
Purchase #4	$114.64	10.822%	$127.0463	$127.05	$127.05	$127.00
Purchase #5	$23.43	13.761%	$26.6542	$26.65	$26.65	$26.70
Purchase #6	$152.52	12.439%	$171.492	$171.49	$171.50	$171.50
Purchase #7	$123.25	6.570%	$131.3475	$131.35	$131.35	$131.30
7 purchase totals =	$779.32		$859.2933	$859.29	$859.30	$859.20