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	$203.45	13.565%	$231.048	$231.05	$231.05	$231.00
Purchase #2	$225.98	6.590%	$240.8721	$240.87	$240.85	$240.90
Purchase #3	$64.80	13.324%	$73.434	$73.43	$73.45	$73.40
Purchase #4	$114.45	11.445%	$127.5488	$127.55	$127.55	$127.50
Purchase #5	$154.32	12.501%	$173.6115	$173.61	$173.60	$173.60
Purchase #6	$193.99	9.543%	$212.5025	$212.50	$212.50	$212.50
Purchase #7	$77.42	6.316%	$82.3098	$82.31	$82.30	$82.30
7 purchase totals =	$1,034.41		$1,141.3267	$1,141.32	$1,141.30	$1,141.20