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	$180.97	10.796%	$200.5075	$200.51	$200.50	$200.50
Purchase #2	$82.82	12.215%	$92.9365	$92.94	$92.95	$92.90
Purchase #3	$75.64	3.733%	$78.4636	$78.46	$78.45	$78.50
Purchase #4	$208.69	10.603%	$230.8174	$230.82	$230.80	$230.80
Purchase #5	$15.90	12.293%	$17.8546	$17.85	$17.85	$17.90
Purchase #6	$224.79	9.626%	$246.4283	$246.43	$246.45	$246.40
Purchase #7	$207.35	4.617%	$216.9233	$216.92	$216.90	$216.90
7 purchase totals =	$996.16		$1,083.9312	$1,083.93	$1,083.90	$1,083.90