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	$159.85	3.306%	$165.1346	$165.13	$165.15	$165.10
Purchase #2	$100.46	7.112%	$107.6047	$107.60	$107.60	$107.60
Purchase #3	$54.57	9.630%	$59.8251	$59.83	$59.85	$59.80
Purchase #4	$208.52	9.719%	$228.7861	$228.79	$228.80	$228.80
Purchase #5	$221.78	6.553%	$236.3132	$236.31	$236.30	$236.30
Purchase #6	$211.89	12.504%	$238.3847	$238.38	$238.40	$238.40
Purchase #7	$197.86	12.270%	$222.1374	$222.14	$222.15	$222.10
7 purchase totals =	$1,154.93		$1,258.1858	$1,258.18	$1,258.25	$1,258.10