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	$120.39	5.742%	$127.3028	$127.30	$127.30	$127.30
Purchase #2	$200.79	7.397%	$215.6424	$215.64	$215.65	$215.60
Purchase #3	$78.73	7.752%	$84.8331	$84.83	$84.85	$84.80
Purchase #4	$179.31	9.396%	$196.158	$196.16	$196.15	$196.20
Purchase #5	$207.30	3.789%	$215.1546	$215.15	$215.15	$215.20
Purchase #6	$212.94	12.159%	$238.8314	$238.83	$238.85	$238.80
Purchase #7	$151.76	6.297%	$161.3163	$161.32	$161.30	$161.30
7 purchase totals =	$1,151.22		$1,239.2386	$1,239.23	$1,239.25	$1,239.20