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	$206.28	11.215%	$229.4143	$229.41	$229.40	$229.40
Purchase #2	$184.86	6.500%	$196.8759	$196.88	$196.90	$196.90
Purchase #3	$103.88	10.338%	$114.6191	$114.62	$114.60	$114.60
Purchase #4	$233.49	11.583%	$260.5351	$260.54	$260.55	$260.50
Purchase #5	$147.84	3.370%	$152.8222	$152.82	$152.80	$152.80
Purchase #6	$59.37	4.761%	$62.1966	$62.20	$62.20	$62.20
Purchase #7	$227.36	13.193%	$257.3556	$257.36	$257.35	$257.40
7 purchase totals =	$1,163.08		$1,273.8188	$1,273.83	$1,273.80	$1,273.80