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	$237.54	9.746%	$260.6906	$260.69	$260.70	$260.70
Purchase #2	$212.84	8.704%	$231.3656	$231.37	$231.35	$231.40
Purchase #3	$144.72	8.386%	$156.8562	$156.86	$156.85	$156.90
Purchase #4	$150.98	9.191%	$164.8566	$164.86	$164.85	$164.90
Purchase #5	$234.73	11.625%	$262.0174	$262.02	$262.00	$262.00
Purchase #6	$88.45	3.462%	$91.5121	$91.51	$91.50	$91.50
Purchase #7	$158.62	8.190%	$171.611	$171.61	$171.60	$171.60
7 purchase totals =	$1,227.88		$1,338.9095	$1,338.92	$1,338.85	$1,339.00