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	$28.57	10.340%	$31.5241	$31.52	$31.50	$31.50
Purchase #2	$114.35	11.798%	$127.841	$127.84	$127.85	$127.80
Purchase #3	$33.45	12.734%	$37.7095	$37.71	$37.70	$37.70
Purchase #4	$79.28	4.204%	$82.6129	$82.61	$82.60	$82.60
Purchase #5	$36.76	9.154%	$40.125	$40.13	$40.15	$40.10
Purchase #6	$12.43	8.735%	$13.5158	$13.52	$13.50	$13.50
Purchase #7	$33.32	6.464%	$35.4738	$35.47	$35.45	$35.50
7 purchase totals =	$338.16		$368.8021	$368.80	$368.75	$368.70