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	$137.54	3.810%	$142.7803	$142.78	$142.80	$142.80
Purchase #2	$23.34	4.641%	$24.4232	$24.42	$24.40	$24.40
Purchase #3	$80.26	11.828%	$89.7532	$89.75	$89.75	$89.80
Purchase #4	$70.34	12.803%	$79.3456	$79.35	$79.35	$79.30
Purchase #5	$40.30	8.530%	$43.7376	$43.74	$43.75	$43.70
Purchase #6	$170.32	12.115%	$190.9543	$190.95	$190.95	$191.00
Purchase #7	$34.39	3.450%	$35.5765	$35.58	$35.60	$35.60
7 purchase totals =	$556.49		$606.5707	$606.57	$606.60	$606.60