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	$203.95	3.233%	$210.5437	$210.54	$210.55	$210.50
Purchase #2	$50.95	9.148%	$55.6109	$55.61	$55.60	$55.60
Purchase #3	$35.90	12.276%	$40.3071	$40.31	$40.30	$40.30
Purchase #4	$52.43	11.626%	$58.5255	$58.53	$58.55	$58.50
Purchase #5	$78.81	12.833%	$88.9237	$88.92	$88.90	$88.90
Purchase #6	$29.45	7.523%	$31.6655	$31.67	$31.65	$31.70
Purchase #7	$24.59	10.834%	$27.2541	$27.25	$27.25	$27.30
7 purchase totals =	$476.08		$512.8305	$512.83	$512.80	$512.80