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	$20.49	6.518%	$21.8255	$21.83	$21.85	$21.80
Purchase #2	$176.42	11.544%	$196.7859	$196.79	$196.80	$196.80
Purchase #3	$214.92	11.769%	$240.2139	$240.21	$240.20	$240.20
Purchase #4	$39.68	7.121%	$42.5056	$42.51	$42.50	$42.50
Purchase #5	$96.31	13.432%	$109.2464	$109.25	$109.25	$109.20
Purchase #6	$148.53	12.127%	$166.5422	$166.54	$166.55	$166.50
Purchase #7	$207.50	6.460%	$220.9045	$220.90	$220.90	$220.90
7 purchase totals =	$903.85		$998.0240	$998.03	$998.05	$997.90