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	$30.75	12.198%	$34.5009	$34.50	$34.50	$34.50
Purchase #2	$158.51	5.168%	$166.7018	$166.70	$166.70	$166.70
Purchase #3	$39.55	8.769%	$43.0181	$43.02	$43.00	$43.00
Purchase #4	$158.43	4.365%	$165.3455	$165.35	$165.35	$165.30
Purchase #5	$221.82	5.274%	$233.5188	$233.52	$233.50	$233.50
Purchase #6	$150.94	11.279%	$167.9645	$167.96	$167.95	$168.00
Purchase #7	$137.47	13.724%	$156.3364	$156.34	$156.35	$156.30
7 purchase totals =	$897.47		$967.3860	$967.39	$967.35	$967.30