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	$114.73	11.302%	$127.6968	$127.70	$127.70	$127.70
Purchase #2	$132.80	5.846%	$140.5635	$140.56	$140.55	$140.60
Purchase #3	$91.46	8.322%	$99.0713	$99.07	$99.05	$99.10
Purchase #4	$74.76	5.381%	$78.7828	$78.78	$78.80	$78.80
Purchase #5	$227.57	9.683%	$249.6056	$249.61	$249.60	$249.60
Purchase #6	$123.51	12.643%	$139.1254	$139.13	$139.15	$139.10
Purchase #7	$14.49	8.672%	$15.7466	$15.75	$15.75	$15.70
7 purchase totals =	$779.32		$850.5920	$850.60	$850.60	$850.60