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	$132.32	6.737%	$141.2344	$141.23	$141.25	$141.20
Purchase #2	$91.82	5.183%	$96.579	$96.58	$96.60	$96.60
Purchase #3	$8.65	13.226%	$9.794	$9.79	$9.80	$9.80
Purchase #4	$137.89	3.797%	$143.1257	$143.13	$143.15	$143.10
Purchase #5	$59.65	13.339%	$67.6067	$67.61	$67.60	$67.60
Purchase #6	$84.52	8.605%	$91.7929	$91.79	$91.80	$91.80
Purchase #7	$56.64	5.716%	$59.8775	$59.88	$59.90	$59.90
7 purchase totals =	$571.49		$610.0102	$610.01	$610.10	$610.00