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	$248.81	12.560%	$280.0605	$280.06	$280.05	$280.10
Purchase #2	$41.66	4.789%	$43.6551	$43.66	$43.65	$43.70
Purchase #3	$182.37	7.844%	$196.6751	$196.68	$196.70	$196.70
Purchase #4	$10.76	11.647%	$12.0132	$12.01	$12.00	$12.00
Purchase #5	$176.98	10.375%	$195.3417	$195.34	$195.35	$195.30
Purchase #6	$173.42	5.260%	$182.5419	$182.54	$182.55	$182.50
Purchase #7	$132.95	5.739%	$140.58	$140.58	$140.60	$140.60
7 purchase totals =	$966.95		$1,050.8675	$1,050.87	$1,050.90	$1,050.90