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	$110.54	9.719%	$121.2834	$121.28	$121.30	$121.30
Purchase #2	$198.67	12.336%	$223.1779	$223.18	$223.20	$223.20
Purchase #3	$138.90	11.560%	$154.9568	$154.96	$154.95	$155.00
Purchase #4	$72.32	8.680%	$78.5974	$78.60	$78.60	$78.60
Purchase #5	$199.78	5.223%	$210.2145	$210.21	$210.20	$210.20
Purchase #6	$97.55	7.233%	$104.6058	$104.61	$104.60	$104.60
Purchase #7	$95.86	4.335%	$100.0155	$100.02	$100.00	$100.00
7 purchase totals =	$913.62		$992.8513	$992.86	$992.85	$992.90