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	$118.54	4.164%	$123.476	$123.48	$123.50	$123.50
Purchase #2	$113.85	8.691%	$123.7447	$123.74	$123.75	$123.70
Purchase #3	$163.43	7.839%	$176.2413	$176.24	$176.25	$176.20
Purchase #4	$76.85	7.641%	$82.7221	$82.72	$82.70	$82.70
Purchase #5	$119.86	9.394%	$131.1196	$131.12	$131.10	$131.10
Purchase #6	$20.53	10.798%	$22.7468	$22.75	$22.75	$22.70
Purchase #7	$127.37	3.276%	$131.5426	$131.54	$131.55	$131.50
7 purchase totals =	$740.43		$791.5931	$791.59	$791.60	$791.40