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	$139.37	6.126%	$147.9078	$147.91	$147.90	$147.90
Purchase #2	$84.94	5.734%	$89.8105	$89.81	$89.80	$89.80
Purchase #3	$153.90	13.856%	$175.2244	$175.22	$175.20	$175.20
Purchase #4	$11.45	9.346%	$12.5201	$12.52	$12.50	$12.50
Purchase #5	$187.88	3.462%	$194.3844	$194.38	$194.40	$194.40
Purchase #6	$120.41	10.701%	$133.2951	$133.30	$133.30	$133.30
Purchase #7	$89.95	9.557%	$98.5465	$98.55	$98.55	$98.50
7 purchase totals =	$787.90		$851.6888	$851.69	$851.65	$851.60