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	$136.91	13.282%	$155.0944	$155.09	$155.10	$155.10
Purchase #2	$201.40	6.696%	$214.8857	$214.89	$214.90	$214.90
Purchase #3	$144.96	11.421%	$161.5159	$161.52	$161.50	$161.50
Purchase #4	$91.86	12.538%	$103.3774	$103.38	$103.40	$103.40
Purchase #5	$128.40	11.563%	$143.2469	$143.25	$143.25	$143.20
Purchase #6	$127.55	3.665%	$132.2247	$132.22	$132.20	$132.20
Purchase #7	$40.96	13.328%	$46.4191	$46.42	$46.40	$46.40
7 purchase totals =	$872.04		$956.7641	$956.77	$956.75	$956.70