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	$48.26	13.822%	$54.9305	$54.93	$54.95	$54.90
Purchase #2	$206.79	7.540%	$222.382	$222.38	$222.40	$222.40
Purchase #3	$100.53	6.448%	$107.0122	$107.01	$107.00	$107.00
Purchase #4	$246.50	10.601%	$272.6315	$272.63	$272.65	$272.60
Purchase #5	$53.29	11.513%	$59.4253	$59.43	$59.45	$59.40
Purchase #6	$50.25	9.730%	$55.1393	$55.14	$55.15	$55.10
Purchase #7	$183.90	12.131%	$206.2089	$206.21	$206.20	$206.20
7 purchase totals =	$889.52		$977.7297	$977.73	$977.80	$977.60