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	$110.31	5.856%	$116.7698	$116.77	$116.75	$116.80
Purchase #2	$56.82	10.827%	$62.9719	$62.97	$62.95	$63.00
Purchase #3	$174.72	12.865%	$197.1977	$197.20	$197.20	$197.20
Purchase #4	$101.91	12.245%	$114.3889	$114.39	$114.40	$114.40
Purchase #5	$72.82	7.719%	$78.441	$78.44	$78.45	$78.40
Purchase #6	$34.61	13.542%	$39.2969	$39.30	$39.30	$39.30
Purchase #7	$183.31	3.848%	$190.3638	$190.36	$190.35	$190.40
7 purchase totals =	$734.50		$799.4300	$799.43	$799.40	$799.50