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	$173.56	4.589%	$181.5247	$181.52	$181.50	$181.50
Purchase #2	$113.89	8.742%	$123.8463	$123.85	$123.85	$123.80
Purchase #3	$217.43	3.831%	$225.7597	$225.76	$225.75	$225.80
Purchase #4	$200.51	7.455%	$215.458	$215.46	$215.45	$215.50
Purchase #5	$218.82	8.269%	$236.9142	$236.91	$236.90	$236.90
Purchase #6	$140.35	5.266%	$147.7408	$147.74	$147.75	$147.70
Purchase #7	$132.26	8.578%	$143.6053	$143.61	$143.60	$143.60
7 purchase totals =	$1,196.82		$1,274.8490	$1,274.85	$1,274.80	$1,274.80