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	$28.89	8.813%	$31.4361	$31.44	$31.45	$31.40
Purchase #2	$99.93	11.481%	$111.403	$111.40	$111.40	$111.40
Purchase #3	$75.78	8.154%	$81.9591	$81.96	$81.95	$82.00
Purchase #4	$100.73	13.656%	$114.4857	$114.49	$114.50	$114.50
Purchase #5	$168.28	8.176%	$182.0386	$182.04	$182.05	$182.00
Purchase #6	$53.41	4.661%	$55.8994	$55.90	$55.90	$55.90
Purchase #7	$56.55	10.515%	$62.4962	$62.50	$62.50	$62.50
7 purchase totals =	$583.57		$639.7181	$639.73	$639.75	$639.70