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	$229.36	11.422%	$255.5575	$255.56	$255.55	$255.60
Purchase #2	$138.67	9.288%	$151.5497	$151.55	$151.55	$151.50
Purchase #3	$193.50	6.450%	$205.9808	$205.98	$206.00	$206.00
Purchase #4	$36.45	13.484%	$41.3649	$41.36	$41.35	$41.40
Purchase #5	$176.31	13.706%	$200.475	$200.48	$200.50	$200.50
Purchase #6	$72.77	6.522%	$77.5161	$77.52	$77.50	$77.50
Purchase #7	$52.52	11.467%	$58.5425	$58.54	$58.55	$58.50
7 purchase totals =	$899.58		$990.9865	$990.99	$991.00	$991.00