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	$233.95	7.461%	$251.405	$251.41	$251.40	$251.40
Purchase #2	$137.94	3.652%	$142.9776	$142.98	$143.00	$143.00
Purchase #3	$44.36	3.312%	$45.8292	$45.83	$45.85	$45.80
Purchase #4	$76.32	10.774%	$84.5427	$84.54	$84.55	$84.50
Purchase #5	$169.48	12.346%	$190.404	$190.40	$190.40	$190.40
Purchase #6	$86.83	13.292%	$98.3714	$98.37	$98.35	$98.40
Purchase #7	$248.62	9.834%	$273.0693	$273.07	$273.05	$273.10
7 purchase totals =	$997.50		$1,086.5992	$1,086.60	$1,086.60	$1,086.60