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	$121.92	5.462%	$128.5793	$128.58	$128.60	$128.60
Purchase #2	$160.50	6.715%	$171.2776	$171.28	$171.30	$171.30
Purchase #3	$129.44	5.105%	$136.0479	$136.05	$136.05	$136.00
Purchase #4	$133.95	6.704%	$142.93	$142.93	$142.95	$142.90
Purchase #5	$75.68	3.567%	$78.3795	$78.38	$78.40	$78.40
Purchase #6	$219.29	10.172%	$241.5962	$241.60	$241.60	$241.60
Purchase #7	$149.70	8.710%	$162.7389	$162.74	$162.75	$162.70
7 purchase totals =	$990.48		$1,061.5494	$1,061.56	$1,061.65	$1,061.50