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	$227.26	9.632%	$249.1497	$249.15	$249.15	$249.10
Purchase #2	$114.78	3.622%	$118.9373	$118.94	$118.95	$118.90
Purchase #3	$124.30	13.771%	$141.4174	$141.42	$141.40	$141.40
Purchase #4	$182.63	4.699%	$191.2118	$191.21	$191.20	$191.20
Purchase #5	$112.96	12.640%	$127.2381	$127.24	$127.25	$127.20
Purchase #6	$98.64	4.155%	$102.7385	$102.74	$102.75	$102.70
Purchase #7	$141.31	4.828%	$148.1324	$148.13	$148.15	$148.10
7 purchase totals =	$1,001.88		$1,078.8252	$1,078.83	$1,078.85	$1,078.60