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	$33.43	13.346%	$37.8916	$37.89	$37.90	$37.90
Purchase #2	$119.42	9.244%	$130.4592	$130.46	$130.45	$130.50
Purchase #3	$239.99	6.826%	$256.3717	$256.37	$256.35	$256.40
Purchase #4	$250.42	11.335%	$278.8051	$278.81	$278.80	$278.80
Purchase #5	$97.68	5.272%	$102.8297	$102.83	$102.85	$102.80
Purchase #6	$92.46	7.693%	$99.5729	$99.57	$99.55	$99.60
Purchase #7	$113.66	9.726%	$124.7146	$124.71	$124.70	$124.70
7 purchase totals =	$947.06		$1,030.6448	$1,030.64	$1,030.60	$1,030.70