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	$151.34	4.347%	$157.9187	$157.92	$157.90	$157.90
Purchase #2	$25.66	9.838%	$28.1844	$28.18	$28.20	$28.20
Purchase #3	$230.33	13.800%	$262.1155	$262.12	$262.10	$262.10
Purchase #4	$47.54	5.758%	$50.2774	$50.28	$50.30	$50.30
Purchase #5	$27.57	3.788%	$28.6144	$28.61	$28.60	$28.60
Purchase #6	$169.89	8.831%	$184.893	$184.89	$184.90	$184.90
Purchase #7	$80.60	12.448%	$90.6331	$90.63	$90.65	$90.60
7 purchase totals =	$732.93		$802.6365	$802.63	$802.65	$802.60