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	$123.47	13.783%	$140.4879	$140.49	$140.50	$140.50
Purchase #2	$150.52	10.744%	$166.6919	$166.69	$166.70	$166.70
Purchase #3	$120.54	3.586%	$124.8626	$124.86	$124.85	$124.90
Purchase #4	$249.50	13.589%	$283.4046	$283.40	$283.40	$283.40
Purchase #5	$110.30	11.841%	$123.3606	$123.36	$123.35	$123.40
Purchase #6	$163.68	13.348%	$185.528	$185.53	$185.55	$185.50
Purchase #7	$100.98	4.503%	$105.5271	$105.53	$105.55	$105.50
7 purchase totals =	$1,018.99		$1,129.8627	$1,129.86	$1,129.90	$1,129.90