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	11.534%	$198.8428	$198.84	$198.85	$198.80
Purchase #2	$156.39	10.580%	$172.9361	$172.94	$172.95	$172.90
Purchase #3	$96.81	5.593%	$102.2246	$102.22	$102.20	$102.20
Purchase #4	$38.34	13.475%	$43.5063	$43.51	$43.50	$43.50
Purchase #5	$219.49	8.724%	$238.6383	$238.64	$238.65	$238.60
Purchase #6	$10.39	13.684%	$11.8118	$11.81	$11.80	$11.80
Purchase #7	$46.85	9.865%	$51.4718	$51.47	$51.45	$51.50
7 purchase totals =	$746.55		$819.4317	$819.43	$819.40	$819.30