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	$122.45	7.278%	$131.3619	$131.36	$131.35	$131.40
Purchase #2	$47.45	8.346%	$51.4102	$51.41	$51.40	$51.40
Purchase #3	$50.66	7.796%	$54.6095	$54.61	$54.60	$54.60
Purchase #4	$222.66	7.164%	$238.6114	$238.61	$238.60	$238.60
Purchase #5	$131.38	12.504%	$147.8078	$147.81	$147.80	$147.80
Purchase #6	$126.96	4.492%	$132.663	$132.66	$132.65	$132.70
Purchase #7	$71.73	7.363%	$77.0115	$77.01	$77.00	$77.00
7 purchase totals =	$773.29		$833.4753	$833.47	$833.40	$833.50