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	$250.68	10.366%	$276.6655	$276.67	$276.65	$276.70
Purchase #2	$41.28	6.779%	$44.0784	$44.08	$44.10	$44.10
Purchase #3	$105.62	6.555%	$112.5434	$112.54	$112.55	$112.50
Purchase #4	$124.49	5.857%	$131.7814	$131.78	$131.80	$131.80
Purchase #5	$50.82	3.225%	$52.4589	$52.46	$52.45	$52.50
Purchase #6	$113.54	12.560%	$127.8006	$127.80	$127.80	$127.80
Purchase #7	$110.51	13.658%	$125.6035	$125.60	$125.60	$125.60
7 purchase totals =	$796.94		$870.9317	$870.93	$870.95	$871.00