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	$201.78	6.867%	$215.6362	$215.64	$215.65	$215.60
Purchase #2	$33.62	3.584%	$34.8249	$34.82	$34.80	$34.80
Purchase #3	$112.88	8.800%	$122.8134	$122.81	$122.80	$122.80
Purchase #4	$143.89	3.419%	$148.8096	$148.81	$148.80	$148.80
Purchase #5	$177.41	10.717%	$196.423	$196.42	$196.40	$196.40
Purchase #6	$37.50	12.675%	$42.2531	$42.25	$42.25	$42.30
Purchase #7	$232.50	12.220%	$260.9115	$260.91	$260.90	$260.90
7 purchase totals =	$939.58		$1,021.6717	$1,021.66	$1,021.60	$1,021.60