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	$231.64	10.301%	$255.5012	$255.50	$255.50	$255.50
Purchase #2	$185.95	13.618%	$211.2727	$211.27	$211.25	$211.30
Purchase #3	$15.62	12.825%	$17.6233	$17.62	$17.60	$17.60
Purchase #4	$154.50	7.228%	$165.6673	$165.67	$165.65	$165.70
Purchase #5	$162.94	9.452%	$178.3411	$178.34	$178.35	$178.30
Purchase #6	$127.37	13.369%	$144.3981	$144.40	$144.40	$144.40
Purchase #7	$175.48	6.637%	$187.1266	$187.13	$187.15	$187.10
7 purchase totals =	$1,053.50		$1,159.9303	$1,159.93	$1,159.90	$1,159.90