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	$43.82	10.619%	$48.4732	$48.47	$48.45	$48.50
Purchase #2	$65.87	4.515%	$68.844	$68.84	$68.85	$68.80
Purchase #3	$40.92	13.437%	$46.4184	$46.42	$46.40	$46.40
Purchase #4	$94.89	5.763%	$100.3585	$100.36	$100.35	$100.40
Purchase #5	$83.88	12.602%	$94.4506	$94.45	$94.45	$94.50
Purchase #6	$185.96	11.169%	$206.7299	$206.73	$206.75	$206.70
Purchase #7	$73.56	6.279%	$78.1788	$78.18	$78.20	$78.20
7 purchase totals =	$588.90		$643.4534	$643.45	$643.45	$643.50