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	$46.47	7.755%	$50.0737	$50.07	$50.05	$50.10
Purchase #2	$176.56	13.235%	$199.9277	$199.93	$199.95	$199.90
Purchase #3	$134.33	4.193%	$139.9625	$139.96	$139.95	$140.00
Purchase #4	$94.57	5.622%	$99.8867	$99.89	$99.90	$99.90
Purchase #5	$19.78	4.176%	$20.606	$20.61	$20.60	$20.60
Purchase #6	$81.59	4.469%	$85.2363	$85.24	$85.25	$85.20
Purchase #7	$78.71	10.723%	$87.1501	$87.15	$87.15	$87.20
7 purchase totals =	$632.01		$682.8430	$682.85	$682.85	$682.90