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	$117.63	3.368%	$121.5918	$121.59	$121.60	$121.60
Purchase #2	$45.54	9.829%	$50.0161	$50.02	$50.00	$50.00
Purchase #3	$106.80	7.589%	$114.9051	$114.91	$114.90	$114.90
Purchase #4	$226.32	5.177%	$238.0366	$238.04	$238.05	$238.00
Purchase #5	$64.95	12.242%	$72.9012	$72.90	$72.90	$72.90
Purchase #6	$106.40	5.151%	$111.8807	$111.88	$111.90	$111.90
Purchase #7	$133.45	10.327%	$147.2314	$147.23	$147.25	$147.20
7 purchase totals =	$801.09		$856.5629	$856.57	$856.60	$856.50