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	$142.47	9.153%	$155.5103	$155.51	$155.50	$155.50
Purchase #2	$132.95	6.519%	$141.617	$141.62	$141.60	$141.60
Purchase #3	$72.79	13.445%	$82.5766	$82.58	$82.60	$82.60
Purchase #4	$176.97	6.363%	$188.2306	$188.23	$188.25	$188.20
Purchase #5	$12.29	8.124%	$13.2884	$13.29	$13.30	$13.30
Purchase #6	$149.78	3.537%	$155.0777	$155.08	$155.10	$155.10
Purchase #7	$90.67	6.846%	$96.8773	$96.88	$96.90	$96.90
7 purchase totals =	$777.92		$833.1779	$833.19	$833.25	$833.20