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	$192.40	12.492%	$216.4346	$216.43	$216.45	$216.40
Purchase #2	$13.60	9.364%	$14.8735	$14.87	$14.85	$14.90
Purchase #3	$38.35	11.184%	$42.6391	$42.64	$42.65	$42.60
Purchase #4	$34.95	7.335%	$37.5136	$37.51	$37.50	$37.50
Purchase #5	$132.87	3.190%	$137.1086	$137.11	$137.10	$137.10
Purchase #6	$171.92	7.681%	$185.1252	$185.13	$185.15	$185.10
Purchase #7	$202.79	10.708%	$224.5048	$224.50	$224.50	$224.50
7 purchase totals =	$786.88		$858.1994	$858.19	$858.20	$858.10