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	$42.43	5.214%	$44.6423	$44.64	$44.65	$44.60
Purchase #2	$181.48	5.766%	$191.9441	$191.94	$191.95	$191.90
Purchase #3	$163.58	12.803%	$184.5231	$184.52	$184.50	$184.50
Purchase #4	$28.47	10.475%	$31.4522	$31.45	$31.45	$31.50
Purchase #5	$37.38	8.719%	$40.6392	$40.64	$40.65	$40.60
Purchase #6	$155.85	13.502%	$176.8929	$176.89	$176.90	$176.90
Purchase #7	$206.80	7.242%	$221.7765	$221.78	$221.80	$221.80
7 purchase totals =	$815.99		$891.8703	$891.86	$891.90	$891.80