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	$99.65	3.855%	$103.4915	$103.49	$103.50	$103.50
Purchase #2	$155.78	3.399%	$161.075	$161.08	$161.10	$161.10
Purchase #3	$67.63	7.313%	$72.5758	$72.58	$72.60	$72.60
Purchase #4	$50.49	7.861%	$54.459	$54.46	$54.45	$54.50
Purchase #5	$124.40	7.161%	$133.3083	$133.31	$133.30	$133.30
Purchase #6	$118.82	8.305%	$128.688	$128.69	$128.70	$128.70
Purchase #7	$105.93	12.590%	$119.2666	$119.27	$119.25	$119.30
7 purchase totals =	$722.70		$772.8642	$772.88	$772.90	$773.00