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	$240.35	3.820%	$249.5314	$249.53	$249.55	$249.50
Purchase #2	$48.61	7.138%	$52.0798	$52.08	$52.10	$52.10
Purchase #3	$155.92	6.733%	$166.4181	$166.42	$166.40	$166.40
Purchase #4	$58.69	13.463%	$66.5914	$66.59	$66.60	$66.60
Purchase #5	$88.60	12.183%	$99.3941	$99.39	$99.40	$99.40
Purchase #6	$159.38	5.568%	$168.2543	$168.25	$168.25	$168.30
Purchase #7	$72.96	9.572%	$79.9437	$79.94	$79.95	$79.90
7 purchase totals =	$824.51		$882.2128	$882.20	$882.25	$882.20