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	$40.96	11.827%	$45.8043	$45.80	$45.80	$45.80
Purchase #2	$62.61	4.556%	$65.4625	$65.46	$65.45	$65.50
Purchase #3	$250.34	4.490%	$261.5803	$261.58	$261.60	$261.60
Purchase #4	$236.35	9.131%	$257.9311	$257.93	$257.95	$257.90
Purchase #5	$78.56	11.140%	$87.3116	$87.31	$87.30	$87.30
Purchase #6	$51.97	11.450%	$57.9206	$57.92	$57.90	$57.90
Purchase #7	$6.34	10.546%	$7.0086	$7.01	$7.00	$7.00
7 purchase totals =	$727.13		$783.0190	$783.01	$783.00	$783.00