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	$122.73	7.690%	$132.1679	$132.17	$132.15	$132.20
Purchase #2	$177.40	4.238%	$184.9182	$184.92	$184.90	$184.90
Purchase #3	$107.33	4.176%	$111.8121	$111.81	$111.80	$111.80
Purchase #4	$217.46	11.391%	$242.2309	$242.23	$242.25	$242.20
Purchase #5	$57.46	12.622%	$64.7126	$64.71	$64.70	$64.70
Purchase #6	$202.47	9.719%	$222.1481	$222.15	$222.15	$222.10
Purchase #7	$145.27	4.423%	$151.6953	$151.70	$151.70	$151.70
7 purchase totals =	$1,030.12		$1,109.6851	$1,109.69	$1,109.65	$1,109.60