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	$47.86	5.296%	$50.3947	$50.39	$50.40	$50.40
Purchase #2	$239.54	6.733%	$255.6682	$255.67	$255.65	$255.70
Purchase #3	$145.98	9.866%	$160.3824	$160.38	$160.40	$160.40
Purchase #4	$99.65	11.559%	$111.1685	$111.17	$111.15	$111.20
Purchase #5	$124.46	10.750%	$137.8395	$137.84	$137.85	$137.80
Purchase #6	$27.64	12.525%	$31.1019	$31.10	$31.10	$31.10
Purchase #7	$196.72	3.641%	$203.8826	$203.88	$203.90	$203.90
7 purchase totals =	$881.85		$950.4378	$950.43	$950.45	$950.50