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	$51.32	10.815%	$56.8703	$56.87	$56.85	$56.90
Purchase #2	$78.54	13.872%	$89.4351	$89.44	$89.45	$89.40
Purchase #3	$121.54	7.117%	$130.19	$130.19	$130.20	$130.20
Purchase #4	$87.76	12.620%	$98.8353	$98.84	$98.85	$98.80
Purchase #5	$192.34	8.351%	$208.4023	$208.40	$208.40	$208.40
Purchase #6	$78.51	12.658%	$88.4478	$88.45	$88.45	$88.40
Purchase #7	$136.42	5.474%	$143.8876	$143.89	$143.90	$143.90
7 purchase totals =	$746.43		$816.0684	$816.08	$816.10	$816.00