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	$139.98	3.537%	$144.9311	$144.93	$144.95	$144.90
Purchase #2	$78.78	4.517%	$82.3385	$82.34	$82.35	$82.30
Purchase #3	$123.55	13.259%	$139.9315	$139.93	$139.95	$139.90
Purchase #4	$246.36	12.594%	$277.3866	$277.39	$277.40	$277.40
Purchase #5	$40.53	6.108%	$43.0056	$43.01	$43.00	$43.00
Purchase #6	$123.57	7.798%	$133.206	$133.21	$133.20	$133.20
Purchase #7	$80.71	7.125%	$86.4606	$86.46	$86.45	$86.50
7 purchase totals =	$833.48		$907.2599	$907.27	$907.30	$907.20