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	$99.38	12.141%	$111.4457	$111.45	$111.45	$111.40
Purchase #2	$234.98	10.664%	$260.0383	$260.04	$260.05	$260.00
Purchase #3	$121.59	9.717%	$133.4049	$133.40	$133.40	$133.40
Purchase #4	$125.83	5.289%	$132.4851	$132.49	$132.50	$132.50
Purchase #5	$79.44	11.306%	$88.4215	$88.42	$88.40	$88.40
Purchase #6	$78.66	6.528%	$83.7949	$83.79	$83.80	$83.80
Purchase #7	$100.41	3.521%	$103.9454	$103.95	$103.95	$103.90
7 purchase totals =	$840.29		$913.5358	$913.54	$913.55	$913.40