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	$150.78	3.493%	$156.0467	$156.05	$156.05	$156.00
Purchase #2	$77.90	6.384%	$82.8731	$82.87	$82.85	$82.90
Purchase #3	$73.58	6.409%	$78.2957	$78.30	$78.30	$78.30
Purchase #4	$176.80	8.339%	$191.5434	$191.54	$191.55	$191.50
Purchase #5	$26.86	5.670%	$28.383	$28.38	$28.40	$28.40
Purchase #6	$162.98	9.712%	$178.8086	$178.81	$178.80	$178.80
Purchase #7	$200.87	11.231%	$223.4297	$223.43	$223.45	$223.40
7 purchase totals =	$869.77		$939.3802	$939.38	$939.40	$939.30