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	$96.69	5.818%	$102.3154	$102.32	$102.30	$102.30
Purchase #2	$126.88	8.691%	$137.9071	$137.91	$137.90	$137.90
Purchase #3	$186.69	9.724%	$204.8437	$204.84	$204.85	$204.80
Purchase #4	$166.28	11.428%	$185.2825	$185.28	$185.30	$185.30
Purchase #5	$233.43	12.292%	$262.1232	$262.12	$262.10	$262.10
Purchase #6	$133.77	5.599%	$141.2598	$141.26	$141.25	$141.30
Purchase #7	$240.27	4.394%	$250.8275	$250.83	$250.85	$250.80
7 purchase totals =	$1,184.01		$1,284.5592	$1,284.56	$1,284.55	$1,284.50