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	$32.73	11.187%	$36.3915	$36.39	$36.40	$36.40
Purchase #2	$138.28	13.415%	$156.8303	$156.83	$156.85	$156.80
Purchase #3	$187.77	9.425%	$205.4673	$205.47	$205.45	$205.50
Purchase #4	$98.44	4.474%	$102.8442	$102.84	$102.85	$102.80
Purchase #5	$144.27	13.771%	$164.1374	$164.14	$164.15	$164.10
Purchase #6	$184.54	3.858%	$191.6596	$191.66	$191.65	$191.70
Purchase #7	$210.71	13.404%	$238.9536	$238.95	$238.95	$239.00
7 purchase totals =	$996.74		$1,096.2839	$1,096.28	$1,096.30	$1,096.30