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	$82.85	9.413%	$90.6487	$90.65	$90.65	$90.60
Purchase #2	$75.97	3.187%	$78.3912	$78.39	$78.40	$78.40
Purchase #3	$32.61	9.738%	$35.7856	$35.79	$35.80	$35.80
Purchase #4	$199.78	6.656%	$213.0774	$213.08	$213.10	$213.10
Purchase #5	$201.73	6.212%	$214.2615	$214.26	$214.25	$214.30
Purchase #6	$9.31	13.798%	$10.5946	$10.59	$10.60	$10.60
Purchase #7	$142.98	3.175%	$147.5196	$147.52	$147.50	$147.50
7 purchase totals =	$745.23		$790.2786	$790.28	$790.30	$790.30