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	$133.99	3.751%	$139.016	$139.02	$139.00	$139.00
Purchase #2	$236.39	10.641%	$261.5443	$261.54	$261.55	$261.50
Purchase #3	$71.68	13.180%	$81.1274	$81.13	$81.15	$81.10
Purchase #4	$219.28	10.227%	$241.7058	$241.71	$241.70	$241.70
Purchase #5	$219.96	6.488%	$234.231	$234.23	$234.25	$234.20
Purchase #6	$127.30	9.699%	$139.6468	$139.65	$139.65	$139.60
Purchase #7	$89.63	10.788%	$99.2993	$99.30	$99.30	$99.30
7 purchase totals =	$1,098.23		$1,196.5706	$1,196.58	$1,196.60	$1,196.40