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	$45.42	6.305%	$48.2837	$48.28	$48.30	$48.30
Purchase #2	$80.46	3.377%	$83.1771	$83.18	$83.20	$83.20
Purchase #3	$45.71	9.654%	$50.1228	$50.12	$50.10	$50.10
Purchase #4	$41.43	4.799%	$43.4182	$43.42	$43.40	$43.40
Purchase #5	$243.85	5.140%	$256.3839	$256.38	$256.40	$256.40
Purchase #6	$121.57	10.102%	$133.851	$133.85	$133.85	$133.90
Purchase #7	$178.41	9.667%	$195.6569	$195.66	$195.65	$195.70
7 purchase totals =	$756.85		$810.8936	$810.89	$810.90	$811.00