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	$73.61	10.652%	$81.4509	$81.45	$81.45	$81.50
Purchase #2	$166.51	11.758%	$186.0882	$186.09	$186.10	$186.10
Purchase #3	$140.77	9.808%	$154.5767	$154.58	$154.60	$154.60
Purchase #4	$55.76	3.620%	$57.7785	$57.78	$57.80	$57.80
Purchase #5	$52.25	13.555%	$59.3325	$59.33	$59.35	$59.30
Purchase #6	$142.80	4.253%	$148.8733	$148.87	$148.85	$148.90
Purchase #7	$246.84	10.549%	$272.8792	$272.88	$272.90	$272.90
7 purchase totals =	$878.54		$960.9793	$960.98	$961.05	$961.10