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	$69.79	5.386%	$73.5489	$73.55	$73.55	$73.50
Purchase #2	$56.58	6.345%	$60.17	$60.17	$60.15	$60.20
Purchase #3	$207.91	8.595%	$225.7799	$225.78	$225.80	$225.80
Purchase #4	$65.85	10.229%	$72.5858	$72.59	$72.60	$72.60
Purchase #5	$117.50	5.145%	$123.5454	$123.55	$123.55	$123.50
Purchase #6	$57.55	13.690%	$65.4286	$65.43	$65.45	$65.40
Purchase #7	$208.96	13.296%	$236.7433	$236.74	$236.75	$236.70
7 purchase totals =	$784.14		$857.8019	$857.81	$857.85	$857.70