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	$177.88	11.863%	$198.9819	$198.98	$199.00	$199.00
Purchase #2	$145.56	12.726%	$164.084	$164.08	$164.10	$164.10
Purchase #3	$113.36	5.504%	$119.5993	$119.60	$119.60	$119.60
Purchase #4	$243.94	11.319%	$271.5516	$271.55	$271.55	$271.60
Purchase #5	$47.60	10.192%	$52.4514	$52.45	$52.45	$52.50
Purchase #6	$90.39	10.771%	$100.1259	$100.13	$100.15	$100.10
Purchase #7	$66.63	8.385%	$72.2169	$72.22	$72.20	$72.20
7 purchase totals =	$885.36		$979.0110	$979.01	$979.05	$979.10