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	$35.61	8.871%	$38.769	$38.77	$38.75	$38.80
Purchase #2	$95.97	5.103%	$100.8673	$100.87	$100.85	$100.90
Purchase #3	$145.29	5.702%	$153.5744	$153.57	$153.55	$153.60
Purchase #4	$242.37	12.590%	$272.8844	$272.88	$272.90	$272.90
Purchase #5	$248.62	12.607%	$279.9635	$279.96	$279.95	$280.00
Purchase #6	$232.42	12.681%	$261.8932	$261.89	$261.90	$261.90
Purchase #7	$143.95	6.180%	$152.8461	$152.85	$152.85	$152.80
7 purchase totals =	$1,144.23		$1,260.7979	$1,260.79	$1,260.75	$1,260.90