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	$34.45	9.128%	$37.5946	$37.59	$37.60	$37.60
Purchase #2	$160.90	6.400%	$171.1976	$171.20	$171.20	$171.20
Purchase #3	$229.46	3.305%	$237.0437	$237.04	$237.05	$237.00
Purchase #4	$199.98	11.164%	$222.3058	$222.31	$222.30	$222.30
Purchase #5	$27.69	7.577%	$29.7881	$29.79	$29.80	$29.80
Purchase #6	$25.41	11.810%	$28.4109	$28.41	$28.40	$28.40
Purchase #7	$100.72	13.333%	$114.149	$114.15	$114.15	$114.10
7 purchase totals =	$778.61		$840.4897	$840.49	$840.50	$840.40