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	$103.34	5.863%	$109.3988	$109.40	$109.40	$109.40
Purchase #2	$120.77	9.351%	$132.0632	$132.06	$132.05	$132.10
Purchase #3	$16.71	13.465%	$18.96	$18.96	$18.95	$19.00
Purchase #4	$42.35	3.156%	$43.6866	$43.69	$43.70	$43.70
Purchase #5	$124.85	5.638%	$131.889	$131.89	$131.90	$131.90
Purchase #6	$113.63	13.173%	$128.5985	$128.60	$128.60	$128.60
Purchase #7	$49.71	6.458%	$52.9203	$52.92	$52.90	$52.90
7 purchase totals =	$571.36		$617.5164	$617.52	$617.50	$617.60