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	$142.75	13.441%	$161.937	$161.94	$161.95	$161.90
Purchase #2	$218.25	10.445%	$241.0462	$241.05	$241.05	$241.00
Purchase #3	$75.49	13.291%	$85.5234	$85.52	$85.50	$85.50
Purchase #4	$11.82	4.814%	$12.389	$12.39	$12.40	$12.40
Purchase #5	$213.34	12.567%	$240.1504	$240.15	$240.15	$240.20
Purchase #6	$87.31	3.444%	$90.317	$90.32	$90.30	$90.30
Purchase #7	$132.70	9.645%	$145.4989	$145.50	$145.50	$145.50
7 purchase totals =	$881.66		$976.8619	$976.87	$976.85	$976.80