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	$145.70	3.293%	$150.4979	$150.50	$150.50	$150.50
Purchase #2	$113.79	9.482%	$124.5796	$124.58	$124.60	$124.60
Purchase #3	$77.47	4.566%	$81.0073	$81.01	$81.00	$81.00
Purchase #4	$104.50	6.625%	$111.4231	$111.42	$111.40	$111.40
Purchase #5	$206.27	13.676%	$234.4795	$234.48	$234.50	$234.50
Purchase #6	$209.56	7.639%	$225.5683	$225.57	$225.55	$225.60
Purchase #7	$112.78	13.535%	$128.0448	$128.04	$128.05	$128.00
7 purchase totals =	$970.07		$1,055.6005	$1,055.60	$1,055.60	$1,055.60