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	$75.25	8.189%	$81.4122	$81.41	$81.40	$81.40
Purchase #2	$105.75	13.385%	$119.9046	$119.90	$119.90	$119.90
Purchase #3	$69.28	13.265%	$78.47	$78.47	$78.45	$78.50
Purchase #4	$178.95	6.107%	$189.8785	$189.88	$189.90	$189.90
Purchase #5	$131.92	12.121%	$147.91	$147.91	$147.90	$147.90
Purchase #6	$123.65	4.170%	$128.8062	$128.81	$128.80	$128.80
Purchase #7	$117.55	8.164%	$127.1468	$127.15	$127.15	$127.10
7 purchase totals =	$802.35		$873.5283	$873.53	$873.50	$873.50