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	$228.78	9.218%	$249.8689	$249.87	$249.85	$249.90
Purchase #2	$139.57	3.837%	$144.9253	$144.93	$144.95	$144.90
Purchase #3	$240.85	11.520%	$268.5959	$268.60	$268.60	$268.60
Purchase #4	$51.83	7.142%	$55.5317	$55.53	$55.55	$55.50
Purchase #5	$142.93	8.389%	$154.9204	$154.92	$154.90	$154.90
Purchase #6	$82.35	10.296%	$90.8288	$90.83	$90.85	$90.80
Purchase #7	$153.70	7.505%	$165.2352	$165.24	$165.25	$165.20
7 purchase totals =	$1,040.01		$1,129.9062	$1,129.92	$1,129.95	$1,129.80