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	$112.38	4.402%	$117.327	$117.33	$117.35	$117.30
Purchase #2	$102.60	12.664%	$115.5933	$115.59	$115.60	$115.60
Purchase #3	$47.76	7.847%	$51.5077	$51.51	$51.50	$51.50
Purchase #4	$250.84	12.133%	$281.2744	$281.27	$281.25	$281.30
Purchase #5	$52.97	12.126%	$59.3931	$59.39	$59.40	$59.40
Purchase #6	$140.80	13.209%	$159.3983	$159.40	$159.40	$159.40
Purchase #7	$43.89	5.857%	$46.4606	$46.46	$46.45	$46.50
7 purchase totals =	$751.24		$830.9544	$830.95	$830.95	$831.00