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	$50.53	11.538%	$56.3602	$56.36	$56.35	$56.40
Purchase #2	$49.30	3.795%	$51.1709	$51.17	$51.15	$51.20
Purchase #3	$5.79	10.171%	$6.3789	$6.38	$6.40	$6.40
Purchase #4	$40.93	4.816%	$42.9012	$42.90	$42.90	$42.90
Purchase #5	$34.89	3.839%	$36.2294	$36.23	$36.25	$36.20
Purchase #6	$69.75	5.185%	$73.3665	$73.37	$73.35	$73.40
Purchase #7	$123.54	7.541%	$132.8562	$132.86	$132.85	$132.90
7 purchase totals =	$374.73		$399.2633	$399.27	$399.25	$399.40