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	$35.25	9.235%	$38.5053	$38.51	$38.50	$38.50
Purchase #2	$206.59	5.811%	$218.5949	$218.59	$218.60	$218.60
Purchase #3	$235.77	9.591%	$258.3827	$258.38	$258.40	$258.40
Purchase #4	$150.79	4.253%	$157.2031	$157.20	$157.20	$157.20
Purchase #5	$152.26	8.640%	$165.4153	$165.42	$165.40	$165.40
Purchase #6	$57.60	3.348%	$59.5284	$59.53	$59.55	$59.50
Purchase #7	$52.57	13.647%	$59.7442	$59.74	$59.75	$59.70
7 purchase totals =	$890.83		$957.3739	$957.37	$957.40	$957.30