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	$164.31	12.461%	$184.7847	$184.78	$184.80	$184.80
Purchase #2	$132.34	13.471%	$150.1675	$150.17	$150.15	$150.20
Purchase #3	$94.29	13.539%	$107.0559	$107.06	$107.05	$107.10
Purchase #4	$50.27	11.669%	$56.136	$56.14	$56.15	$56.10
Purchase #5	$38.60	5.742%	$40.8164	$40.82	$40.80	$40.80
Purchase #6	$54.37	4.543%	$56.84	$56.84	$56.85	$56.80
Purchase #7	$210.46	13.287%	$238.4238	$238.42	$238.40	$238.40
7 purchase totals =	$744.64		$834.2243	$834.23	$834.20	$834.20