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	$150.75	9.234%	$164.6703	$164.67	$164.65	$164.70
Purchase #2	$100.74	10.862%	$111.6824	$111.68	$111.70	$111.70
Purchase #3	$59.66	13.289%	$67.5882	$67.59	$67.60	$67.60
Purchase #4	$223.43	4.759%	$234.063	$234.06	$234.05	$234.10
Purchase #5	$202.87	13.725%	$230.7139	$230.71	$230.70	$230.70
Purchase #6	$236.35	10.414%	$260.9635	$260.96	$260.95	$261.00
Purchase #7	$136.89	10.762%	$151.6221	$151.62	$151.60	$151.60
7 purchase totals =	$1,110.69		$1,221.3034	$1,221.29	$1,221.25	$1,221.40