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	$39.59	6.336%	$42.0984	$42.10	$42.10	$42.10
Purchase #2	$218.71	3.772%	$226.9597	$226.96	$226.95	$227.00
Purchase #3	$118.50	3.872%	$123.0883	$123.09	$123.10	$123.10
Purchase #4	$236.91	8.123%	$256.1542	$256.15	$256.15	$256.20
Purchase #5	$21.90	12.110%	$24.5521	$24.55	$24.55	$24.60
Purchase #6	$50.42	6.131%	$53.5113	$53.51	$53.50	$53.50
Purchase #7	$97.93	11.745%	$109.4319	$109.43	$109.45	$109.40
7 purchase totals =	$783.96		$835.7959	$835.79	$835.80	$835.90