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	$155.77	12.249%	$174.8503	$174.85	$174.85	$174.90
Purchase #2	$203.60	13.685%	$231.4627	$231.46	$231.45	$231.50
Purchase #3	$139.58	12.242%	$156.6674	$156.67	$156.65	$156.70
Purchase #4	$52.93	13.351%	$59.9967	$60.00	$60.00	$60.00
Purchase #5	$140.97	10.562%	$155.8593	$155.86	$155.85	$155.90
Purchase #6	$76.86	4.780%	$80.5339	$80.53	$80.55	$80.50
Purchase #7	$139.70	10.494%	$154.3601	$154.36	$154.35	$154.40
7 purchase totals =	$909.41		$1,013.7304	$1,013.73	$1,013.70	$1,013.90