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	$118.83	4.747%	$124.4709	$124.47	$124.45	$124.50
Purchase #2	$35.46	13.492%	$40.2443	$40.24	$40.25	$40.20
Purchase #3	$218.69	10.737%	$242.1707	$242.17	$242.15	$242.20
Purchase #4	$69.67	5.667%	$73.6182	$73.62	$73.60	$73.60
Purchase #5	$120.31	6.828%	$128.5248	$128.52	$128.50	$128.50
Purchase #6	$178.91	7.771%	$192.8131	$192.81	$192.80	$192.80
Purchase #7	$78.31	4.121%	$81.5372	$81.54	$81.55	$81.50
7 purchase totals =	$820.18		$883.3792	$883.37	$883.30	$883.30