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	$230.78	12.273%	$259.1036	$259.10	$259.10	$259.10
Purchase #2	$186.67	11.652%	$208.4208	$208.42	$208.40	$208.40
Purchase #3	$19.93	11.493%	$22.2206	$22.22	$22.20	$22.20
Purchase #4	$100.66	12.575%	$113.318	$113.32	$113.30	$113.30
Purchase #5	$38.95	10.102%	$42.8847	$42.88	$42.90	$42.90
Purchase #6	$210.37	3.847%	$218.4629	$218.46	$218.45	$218.50
Purchase #7	$136.37	10.628%	$150.8634	$150.86	$150.85	$150.90
7 purchase totals =	$923.73		$1,015.2740	$1,015.26	$1,015.20	$1,015.30