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	$29.25	7.821%	$31.5376	$31.54	$31.55	$31.50
Purchase #2	$117.46	12.657%	$132.3269	$132.33	$132.35	$132.30
Purchase #3	$17.98	8.465%	$19.502	$19.50	$19.50	$19.50
Purchase #4	$177.60	3.395%	$183.6295	$183.63	$183.65	$183.60
Purchase #5	$18.41	10.398%	$20.3243	$20.32	$20.30	$20.30
Purchase #6	$169.32	12.520%	$190.5189	$190.52	$190.50	$190.50
Purchase #7	$53.81	7.507%	$57.8495	$57.85	$57.85	$57.80
7 purchase totals =	$583.83		$635.6887	$635.69	$635.70	$635.50