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	$246.45	13.857%	$280.6006	$280.60	$280.60	$280.60
Purchase #2	$86.89	7.220%	$93.1635	$93.16	$93.15	$93.20
Purchase #3	$96.72	7.820%	$104.2835	$104.28	$104.30	$104.30
Purchase #4	$227.46	4.365%	$237.3886	$237.39	$237.40	$237.40
Purchase #5	$59.43	3.134%	$61.2925	$61.29	$61.30	$61.30
Purchase #6	$17.67	7.164%	$18.9359	$18.94	$18.95	$18.90
Purchase #7	$185.50	10.800%	$205.534	$205.53	$205.55	$205.50
7 purchase totals =	$920.12		$1,001.1986	$1,001.19	$1,001.25	$1,001.20