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	$37.66	13.169%	$42.6194	$42.62	$42.60	$42.60
Purchase #2	$102.48	6.451%	$109.091	$109.09	$109.10	$109.10
Purchase #3	$75.99	6.448%	$80.8898	$80.89	$80.90	$80.90
Purchase #4	$162.38	7.239%	$174.1347	$174.13	$174.15	$174.10
Purchase #5	$95.72	4.665%	$100.1853	$100.19	$100.20	$100.20
Purchase #6	$43.91	13.209%	$49.7101	$49.71	$49.70	$49.70
Purchase #7	$55.36	13.485%	$62.8253	$62.83	$62.85	$62.80
7 purchase totals =	$573.50		$619.4556	$619.46	$619.50	$619.40