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	$178.28	10.150%	$196.3754	$196.38	$196.40	$196.40
Purchase #2	$236.57	11.144%	$262.9334	$262.93	$262.95	$262.90
Purchase #3	$156.65	8.259%	$169.5877	$169.59	$169.60	$169.60
Purchase #4	$125.86	10.733%	$139.3686	$139.37	$139.35	$139.40
Purchase #5	$207.84	5.665%	$219.6141	$219.61	$219.60	$219.60
Purchase #6	$91.60	5.418%	$96.5629	$96.56	$96.55	$96.60
Purchase #7	$137.38	13.648%	$156.1296	$156.13	$156.15	$156.10
7 purchase totals =	$1,134.18		$1,240.5717	$1,240.57	$1,240.60	$1,240.60