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	$241.65	3.420%	$249.9144	$249.91	$249.90	$249.90
Purchase #2	$126.92	8.687%	$137.9455	$137.95	$137.95	$137.90
Purchase #3	$40.69	6.384%	$43.2876	$43.29	$43.30	$43.30
Purchase #4	$116.39	8.411%	$126.1796	$126.18	$126.20	$126.20
Purchase #5	$172.59	12.552%	$194.2535	$194.25	$194.25	$194.30
Purchase #6	$154.44	11.739%	$172.5697	$172.57	$172.55	$172.60
Purchase #7	$51.76	5.397%	$54.5535	$54.55	$54.55	$54.60
7 purchase totals =	$904.44		$978.7038	$978.70	$978.70	$978.80