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	$37.97	7.708%	$40.8967	$40.90	$40.90	$40.90
Purchase #2	$228.94	12.351%	$257.2164	$257.22	$257.20	$257.20
Purchase #3	$180.32	8.361%	$195.3966	$195.40	$195.40	$195.40
Purchase #4	$175.25	12.330%	$196.8583	$196.86	$196.85	$196.90
Purchase #5	$50.86	6.702%	$54.2686	$54.27	$54.25	$54.30
Purchase #6	$72.59	9.745%	$79.6639	$79.66	$79.65	$79.70
Purchase #7	$116.99	13.619%	$132.9229	$132.92	$132.90	$132.90
7 purchase totals =	$862.92		$957.2234	$957.23	$957.15	$957.30