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	$128.67	8.526%	$139.6404	$139.64	$139.65	$139.60
Purchase #2	$94.25	9.685%	$103.3781	$103.38	$103.40	$103.40
Purchase #3	$177.78	11.752%	$198.6727	$198.67	$198.65	$198.70
Purchase #4	$77.97	5.663%	$82.3854	$82.39	$82.40	$82.40
Purchase #5	$55.26	3.411%	$57.1449	$57.14	$57.15	$57.10
Purchase #6	$219.81	13.603%	$249.7108	$249.71	$249.70	$249.70
Purchase #7	$172.42	5.724%	$182.2893	$182.29	$182.30	$182.30
7 purchase totals =	$926.16		$1,013.2216	$1,013.22	$1,013.25	$1,013.20