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	$176.67	12.130%	$198.1001	$198.10	$198.10	$198.10
Purchase #2	$49.25	4.667%	$51.5485	$51.55	$51.55	$51.50
Purchase #3	$145.67	6.229%	$154.7438	$154.74	$154.75	$154.70
Purchase #4	$241.45	5.287%	$254.2155	$254.22	$254.20	$254.20
Purchase #5	$76.46	7.751%	$82.3864	$82.39	$82.40	$82.40
Purchase #6	$45.31	5.650%	$47.87	$47.87	$47.85	$47.90
Purchase #7	$135.64	5.830%	$143.5478	$143.55	$143.55	$143.50
7 purchase totals =	$870.45		$932.4121	$932.42	$932.40	$932.30