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	$44.87	11.524%	$50.0408	$50.04	$50.05	$50.00
Purchase #2	$157.91	6.150%	$167.6215	$167.62	$167.60	$167.60
Purchase #3	$43.86	9.141%	$47.8692	$47.87	$47.85	$47.90
Purchase #4	$92.72	6.264%	$98.528	$98.53	$98.55	$98.50
Purchase #5	$37.76	7.545%	$40.609	$40.61	$40.60	$40.60
Purchase #6	$248.57	6.312%	$264.2597	$264.26	$264.25	$264.30
Purchase #7	$47.92	3.467%	$49.5814	$49.58	$49.60	$49.60
7 purchase totals =	$673.61		$718.5096	$718.51	$718.50	$718.50