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	$133.92	7.294%	$143.6881	$143.69	$143.70	$143.70
Purchase #2	$39.39	4.436%	$41.1373	$41.14	$41.15	$41.10
Purchase #3	$10.99	8.546%	$11.9292	$11.93	$11.95	$11.90
Purchase #4	$116.85	12.357%	$131.2892	$131.29	$131.30	$131.30
Purchase #5	$39.27	13.866%	$44.7152	$44.72	$44.70	$44.70
Purchase #6	$38.35	12.705%	$43.2224	$43.22	$43.20	$43.20
Purchase #7	$39.53	6.543%	$42.1164	$42.12	$42.10	$42.10
7 purchase totals =	$418.30		$458.0978	$458.11	$458.10	$458.00