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	$219.98	9.217%	$240.2556	$240.26	$240.25	$240.30
Purchase #2	$172.59	6.598%	$183.9775	$183.98	$184.00	$184.00
Purchase #3	$57.93	9.423%	$63.3887	$63.39	$63.40	$63.40
Purchase #4	$226.54	5.187%	$238.2906	$238.29	$238.30	$238.30
Purchase #5	$75.60	6.268%	$80.3386	$80.34	$80.35	$80.30
Purchase #6	$73.39	13.317%	$83.1633	$83.16	$83.15	$83.20
Purchase #7	$88.80	12.477%	$99.8796	$99.88	$99.90	$99.90
7 purchase totals =	$914.83		$989.2939	$989.30	$989.35	$989.40