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	$24.89	13.761%	$28.3151	$28.32	$28.30	$28.30
Purchase #2	$17.78	6.129%	$18.8697	$18.87	$18.85	$18.90
Purchase #3	$13.60	5.444%	$14.3404	$14.34	$14.35	$14.30
Purchase #4	$37.31	3.743%	$38.7065	$38.71	$38.70	$38.70
Purchase #5	$140.50	11.190%	$156.222	$156.22	$156.20	$156.20
Purchase #6	$244.32	4.310%	$254.8502	$254.85	$254.85	$254.90
Purchase #7	$102.51	13.580%	$116.4309	$116.43	$116.45	$116.40
7 purchase totals =	$580.91		$627.7348	$627.74	$627.70	$627.70