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	$177.69	5.555%	$187.5607	$187.56	$187.55	$187.60
Purchase #2	$201.72	10.664%	$223.2314	$223.23	$223.25	$223.20
Purchase #3	$51.61	12.264%	$57.9395	$57.94	$57.95	$57.90
Purchase #4	$142.25	11.372%	$158.4267	$158.43	$158.45	$158.40
Purchase #5	$84.75	9.304%	$92.6351	$92.64	$92.65	$92.60
Purchase #6	$39.79	7.334%	$42.7082	$42.71	$42.70	$42.70
Purchase #7	$14.64	7.806%	$15.7828	$15.78	$15.80	$15.80
7 purchase totals =	$712.45		$778.2844	$778.29	$778.35	$778.20