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	$150.91	3.715%	$156.5163	$156.52	$156.50	$156.50
Purchase #2	$64.40	4.763%	$67.4674	$67.47	$67.45	$67.50
Purchase #3	$200.97	10.780%	$222.6346	$222.63	$222.65	$222.60
Purchase #4	$133.51	13.357%	$151.3429	$151.34	$151.35	$151.30
Purchase #5	$162.49	8.598%	$176.4609	$176.46	$176.45	$176.50
Purchase #6	$138.80	8.508%	$150.6091	$150.61	$150.60	$150.60
Purchase #7	$180.30	5.559%	$190.3229	$190.32	$190.30	$190.30
7 purchase totals =	$1,031.38		$1,115.3541	$1,115.35	$1,115.30	$1,115.30