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	$175.89	4.828%	$184.382	$184.38	$184.40	$184.40
Purchase #2	$182.70	9.377%	$199.8318	$199.83	$199.85	$199.80
Purchase #3	$15.68	5.327%	$16.5153	$16.52	$16.50	$16.50
Purchase #4	$96.55	7.244%	$103.5441	$103.54	$103.55	$103.50
Purchase #5	$54.33	9.665%	$59.581	$59.58	$59.60	$59.60
Purchase #6	$234.85	10.694%	$259.9649	$259.96	$259.95	$260.00
Purchase #7	$139.71	5.683%	$147.6497	$147.65	$147.65	$147.60
7 purchase totals =	$899.71		$971.4688	$971.46	$971.50	$971.40