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	$129.55	7.621%	$139.423	$139.42	$139.40	$139.40
Purchase #2	$174.49	11.874%	$195.2089	$195.21	$195.20	$195.20
Purchase #3	$71.50	9.469%	$78.2703	$78.27	$78.25	$78.30
Purchase #4	$111.39	3.628%	$115.4312	$115.43	$115.45	$115.40
Purchase #5	$65.82	10.807%	$72.9332	$72.93	$72.95	$72.90
Purchase #6	$74.29	11.487%	$82.8237	$82.82	$82.80	$82.80
Purchase #7	$145.68	3.417%	$150.6579	$150.66	$150.65	$150.70
7 purchase totals =	$772.72		$834.7482	$834.74	$834.70	$834.70