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	$35.73	4.872%	$37.4708	$37.47	$37.45	$37.50
Purchase #2	$127.80	10.207%	$140.8445	$140.84	$140.85	$140.80
Purchase #3	$105.81	10.369%	$116.7814	$116.78	$116.80	$116.80
Purchase #4	$109.53	8.278%	$118.5969	$118.60	$118.60	$118.60
Purchase #5	$192.79	12.834%	$217.5327	$217.53	$217.55	$217.50
Purchase #6	$169.91	6.277%	$180.5753	$180.58	$180.60	$180.60
Purchase #7	$228.38	4.617%	$238.9243	$238.92	$238.90	$238.90
7 purchase totals =	$969.95		$1,050.7259	$1,050.72	$1,050.75	$1,050.70