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	$38.45	10.688%	$42.5595	$42.56	$42.55	$42.60
Purchase #2	$151.78	5.114%	$159.542	$159.54	$159.55	$159.50
Purchase #3	$162.66	10.716%	$180.0906	$180.09	$180.10	$180.10
Purchase #4	$168.86	6.270%	$179.4475	$179.45	$179.45	$179.40
Purchase #5	$68.44	3.408%	$70.7724	$70.77	$70.75	$70.80
Purchase #6	$204.40	10.140%	$225.1262	$225.13	$225.15	$225.10
Purchase #7	$90.69	13.632%	$103.0529	$103.05	$103.05	$103.10
7 purchase totals =	$885.28		$960.5911	$960.59	$960.60	$960.60