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	$246.92	4.538%	$258.1252	$258.13	$258.15	$258.10
Purchase #2	$164.61	10.724%	$182.2628	$182.26	$182.25	$182.30
Purchase #3	$171.84	13.440%	$194.9353	$194.94	$194.95	$194.90
Purchase #4	$123.55	12.844%	$139.4188	$139.42	$139.40	$139.40
Purchase #5	$187.33	12.136%	$210.0644	$210.06	$210.05	$210.10
Purchase #6	$92.28	9.132%	$100.707	$100.71	$100.70	$100.70
Purchase #7	$90.46	3.798%	$93.8957	$93.90	$93.90	$93.90
7 purchase totals =	$1,076.99		$1,179.4092	$1,179.42	$1,179.40	$1,179.40