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	$50.52	8.652%	$54.891	$54.89	$54.90	$54.90
Purchase #2	$139.51	8.580%	$151.48	$151.48	$151.50	$151.50
Purchase #3	$126.57	12.594%	$142.5102	$142.51	$142.50	$142.50
Purchase #4	$35.48	7.312%	$38.0743	$38.07	$38.05	$38.10
Purchase #5	$136.56	4.564%	$142.7926	$142.79	$142.80	$142.80
Purchase #6	$32.79	4.627%	$34.3072	$34.31	$34.30	$34.30
Purchase #7	$70.29	5.455%	$74.1243	$74.12	$74.10	$74.10
7 purchase totals =	$591.72		$638.1796	$638.17	$638.15	$638.20