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	$41.80	11.748%	$46.7107	$46.71	$46.70	$46.70
Purchase #2	$241.84	10.620%	$267.5234	$267.52	$267.50	$267.50
Purchase #3	$95.98	3.721%	$99.5514	$99.55	$99.55	$99.60
Purchase #4	$59.87	10.494%	$66.1528	$66.15	$66.15	$66.20
Purchase #5	$178.69	4.654%	$187.0062	$187.01	$187.00	$187.00
Purchase #6	$123.25	4.161%	$128.3784	$128.38	$128.40	$128.40
Purchase #7	$125.95	4.510%	$131.6303	$131.63	$131.65	$131.60
7 purchase totals =	$867.38		$926.9532	$926.95	$926.95	$927.00