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	$177.39	4.648%	$185.6351	$185.64	$185.65	$185.60
Purchase #2	$129.39	5.355%	$136.3188	$136.32	$136.30	$136.30
Purchase #3	$49.53	12.157%	$55.5514	$55.55	$55.55	$55.60
Purchase #4	$6.70	6.579%	$7.1408	$7.14	$7.15	$7.10
Purchase #5	$242.73	6.798%	$259.2308	$259.23	$259.25	$259.20
Purchase #6	$34.30	11.212%	$38.1457	$38.15	$38.15	$38.10
Purchase #7	$79.42	12.670%	$89.4825	$89.48	$89.50	$89.50
7 purchase totals =	$719.46		$771.5051	$771.51	$771.55	$771.40