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	$240.93	13.611%	$273.723	$273.72	$273.70	$273.70
Purchase #2	$136.34	10.257%	$150.3244	$150.32	$150.30	$150.30
Purchase #3	$105.67	12.433%	$118.808	$118.81	$118.80	$118.80
Purchase #4	$40.57	8.337%	$43.9523	$43.95	$43.95	$44.00
Purchase #5	$138.76	9.173%	$151.4885	$151.49	$151.50	$151.50
Purchase #6	$71.33	3.164%	$73.5869	$73.59	$73.60	$73.60
Purchase #7	$240.56	8.707%	$261.5056	$261.51	$261.50	$261.50
7 purchase totals =	$974.16		$1,073.3887	$1,073.39	$1,073.35	$1,073.40