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	$181.99	12.650%	$205.0117	$205.01	$205.00	$205.00
Purchase #2	$216.53	12.124%	$242.7821	$242.78	$242.80	$242.80
Purchase #3	$248.67	4.359%	$259.5095	$259.51	$259.50	$259.50
Purchase #4	$137.69	4.821%	$144.328	$144.33	$144.35	$144.30
Purchase #5	$137.86	4.572%	$144.163	$144.16	$144.15	$144.20
Purchase #6	$50.88	9.844%	$55.8886	$55.89	$55.90	$55.90
Purchase #7	$230.29	3.444%	$238.2212	$238.22	$238.20	$238.20
7 purchase totals =	$1,203.91		$1,289.9041	$1,289.90	$1,289.90	$1,289.90