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	$87.51	5.298%	$92.1463	$92.15	$92.15	$92.10
Purchase #2	$111.92	12.448%	$125.8518	$125.85	$125.85	$125.90
Purchase #3	$98.96	4.359%	$103.2737	$103.27	$103.25	$103.30
Purchase #4	$13.45	3.716%	$13.9498	$13.95	$13.95	$13.90
Purchase #5	$239.50	12.142%	$268.5801	$268.58	$268.60	$268.60
Purchase #6	$31.89	5.597%	$33.6749	$33.67	$33.65	$33.70
Purchase #7	$241.93	9.726%	$265.4601	$265.46	$265.45	$265.50
7 purchase totals =	$825.16		$902.9367	$902.93	$902.90	$903.00