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	$169.78	3.755%	$176.1552	$176.16	$176.15	$176.20
Purchase #2	$164.89	12.400%	$185.3364	$185.34	$185.35	$185.30
Purchase #3	$197.81	3.724%	$205.1764	$205.18	$205.20	$205.20
Purchase #4	$142.68	12.448%	$160.4408	$160.44	$160.45	$160.40
Purchase #5	$58.49	13.853%	$66.5926	$66.59	$66.60	$66.60
Purchase #6	$51.46	10.549%	$56.8885	$56.89	$56.90	$56.90
Purchase #7	$84.76	4.802%	$88.8302	$88.83	$88.85	$88.80
7 purchase totals =	$869.87		$939.4201	$939.43	$939.50	$939.40