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	$219.45	9.378%	$240.03	$240.03	$240.05	$240.00
Purchase #2	$171.47	4.118%	$178.5311	$178.53	$178.55	$178.50
Purchase #3	$176.61	8.591%	$191.7826	$191.78	$191.80	$191.80
Purchase #4	$94.67	6.493%	$100.8169	$100.82	$100.80	$100.80
Purchase #5	$188.53	4.462%	$196.9422	$196.94	$196.95	$196.90
Purchase #6	$78.96	4.246%	$82.3126	$82.31	$82.30	$82.30
Purchase #7	$23.32	13.228%	$26.4048	$26.40	$26.40	$26.40
7 purchase totals =	$953.01		$1,016.8202	$1,016.81	$1,016.85	$1,016.70