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	$50.80	3.289%	$52.4708	$52.47	$52.45	$52.50
Purchase #2	$163.85	9.318%	$179.1175	$179.12	$179.10	$179.10
Purchase #3	$146.57	12.795%	$165.3236	$165.32	$165.30	$165.30
Purchase #4	$231.90	4.300%	$241.8717	$241.87	$241.85	$241.90
Purchase #5	$170.76	9.707%	$187.3357	$187.34	$187.35	$187.30
Purchase #6	$82.53	9.627%	$90.4752	$90.48	$90.50	$90.50
Purchase #7	$58.99	6.686%	$62.9341	$62.93	$62.95	$62.90
7 purchase totals =	$905.40		$979.5286	$979.53	$979.50	$979.50