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	$249.35	7.823%	$268.8567	$268.86	$268.85	$268.90
Purchase #2	$72.49	13.491%	$82.2696	$82.27	$82.25	$82.30
Purchase #3	$62.55	7.551%	$67.2732	$67.27	$67.25	$67.30
Purchase #4	$21.69	3.612%	$22.4734	$22.47	$22.45	$22.50
Purchase #5	$161.34	6.267%	$171.4512	$171.45	$171.45	$171.50
Purchase #6	$43.42	7.509%	$46.6804	$46.68	$46.70	$46.70
Purchase #7	$126.93	11.706%	$141.7884	$141.79	$141.80	$141.80
7 purchase totals =	$737.77		$800.7929	$800.79	$800.75	$801.00