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	$91.79	12.209%	$102.9966	$103.00	$103.00	$103.00
Purchase #2	$59.57	11.847%	$66.6273	$66.63	$66.65	$66.60
Purchase #3	$189.82	4.806%	$198.9427	$198.94	$198.95	$198.90
Purchase #4	$242.69	3.366%	$250.8589	$250.86	$250.85	$250.90
Purchase #5	$133.58	10.631%	$147.7809	$147.78	$147.80	$147.80
Purchase #6	$113.39	13.498%	$128.6954	$128.70	$128.70	$128.70
Purchase #7	$112.43	3.583%	$116.4584	$116.46	$116.45	$116.50
7 purchase totals =	$943.27		$1,012.3602	$1,012.37	$1,012.40	$1,012.40