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	$77.79	4.278%	$81.1179	$81.12	$81.10	$81.10
Purchase #2	$30.71	3.644%	$31.8291	$31.83	$31.85	$31.80
Purchase #3	$146.61	12.544%	$165.0008	$165.00	$165.00	$165.00
Purchase #4	$75.45	4.186%	$78.6083	$78.61	$78.60	$78.60
Purchase #5	$102.94	10.872%	$114.1316	$114.13	$114.15	$114.10
Purchase #6	$35.81	10.544%	$39.5858	$39.59	$39.60	$39.60
Purchase #7	$118.60	7.755%	$127.7974	$127.80	$127.80	$127.80
7 purchase totals =	$587.91		$638.0709	$638.08	$638.10	$638.00