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	$227.68	10.315%	$251.1652	$251.17	$251.15	$251.20
Purchase #2	$166.51	9.494%	$182.3185	$182.32	$182.30	$182.30
Purchase #3	$222.77	10.628%	$246.446	$246.45	$246.45	$246.40
Purchase #4	$241.31	5.237%	$253.9474	$253.95	$253.95	$253.90
Purchase #5	$37.41	7.838%	$40.3422	$40.34	$40.35	$40.30
Purchase #6	$121.42	8.163%	$131.3315	$131.33	$131.35	$131.30
Purchase #7	$63.35	3.566%	$65.6091	$65.61	$65.60	$65.60
7 purchase totals =	$1,080.45		$1,171.1599	$1,171.17	$1,171.15	$1,171.00