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	$5.88	12.209%	$6.5979	$6.60	$6.60	$6.60
Purchase #2	$68.58	5.737%	$72.5144	$72.51	$72.50	$72.50
Purchase #3	$211.31	12.786%	$238.3281	$238.33	$238.35	$238.30
Purchase #4	$79.49	9.849%	$87.319	$87.32	$87.30	$87.30
Purchase #5	$141.93	7.591%	$152.7039	$152.70	$152.70	$152.70
Purchase #6	$162.90	6.636%	$173.71	$173.71	$173.70	$173.70
Purchase #7	$177.64	10.550%	$196.381	$196.38	$196.40	$196.40
7 purchase totals =	$847.73		$927.5543	$927.55	$927.55	$927.50