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	$38.68	11.491%	$43.1247	$43.12	$43.10	$43.10
Purchase #2	$121.77	10.642%	$134.7288	$134.73	$134.75	$134.70
Purchase #3	$218.54	4.454%	$228.2738	$228.27	$228.25	$228.30
Purchase #4	$239.41	11.669%	$267.3468	$267.35	$267.35	$267.30
Purchase #5	$164.39	12.796%	$185.4253	$185.43	$185.45	$185.40
Purchase #6	$78.75	3.806%	$81.7472	$81.75	$81.75	$81.70
Purchase #7	$137.80	5.150%	$144.8967	$144.90	$144.90	$144.90
7 purchase totals =	$999.34		$1,085.5433	$1,085.55	$1,085.55	$1,085.40