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	$28.85	9.302%	$31.5336	$31.53	$31.55	$31.50
Purchase #2	$79.57	7.336%	$85.4073	$85.41	$85.40	$85.40
Purchase #3	$111.42	12.646%	$125.5102	$125.51	$125.50	$125.50
Purchase #4	$38.89	4.649%	$40.698	$40.70	$40.70	$40.70
Purchase #5	$119.80	3.837%	$124.3967	$124.40	$124.40	$124.40
Purchase #6	$96.59	12.152%	$108.3276	$108.33	$108.35	$108.30
Purchase #7	$213.65	4.178%	$222.5763	$222.58	$222.60	$222.60
7 purchase totals =	$688.77		$738.4497	$738.46	$738.50	$738.40