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	$81.51	12.338%	$91.5667	$91.57	$91.55	$91.60
Purchase #2	$91.50	13.512%	$103.8635	$103.86	$103.85	$103.90
Purchase #3	$108.92	13.350%	$123.4608	$123.46	$123.45	$123.50
Purchase #4	$133.66	3.701%	$138.6068	$138.61	$138.60	$138.60
Purchase #5	$100.77	6.672%	$107.4934	$107.49	$107.50	$107.50
Purchase #6	$161.47	13.492%	$183.2555	$183.26	$183.25	$183.30
Purchase #7	$28.60	13.470%	$32.4524	$32.45	$32.45	$32.50
7 purchase totals =	$706.43		$780.6991	$780.70	$780.65	$780.90