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	$249.42	10.608%	$275.8785	$275.88	$275.90	$275.90
Purchase #2	$122.70	7.191%	$131.5234	$131.52	$131.50	$131.50
Purchase #3	$75.89	4.492%	$79.299	$79.30	$79.30	$79.30
Purchase #4	$19.79	5.372%	$20.8531	$20.85	$20.85	$20.90
Purchase #5	$67.77	13.249%	$76.7488	$76.75	$76.75	$76.70
Purchase #6	$124.27	10.136%	$136.866	$136.87	$136.85	$136.90
Purchase #7	$48.76	5.349%	$51.3682	$51.37	$51.35	$51.40
7 purchase totals =	$708.60		$772.5370	$772.54	$772.50	$772.60