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	$34.25	10.752%	$37.9326	$37.93	$37.95	$37.90
Purchase #2	$210.75	12.450%	$236.9884	$236.99	$237.00	$237.00
Purchase #3	$52.31	3.248%	$54.009	$54.01	$54.00	$54.00
Purchase #4	$192.78	8.364%	$208.9041	$208.90	$208.90	$208.90
Purchase #5	$56.90	9.735%	$62.4392	$62.44	$62.45	$62.40
Purchase #6	$84.25	7.258%	$90.3649	$90.36	$90.35	$90.40
Purchase #7	$247.42	13.408%	$280.5941	$280.59	$280.60	$280.60
7 purchase totals =	$878.66		$971.2323	$971.22	$971.25	$971.20