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	$120.81	13.798%	$137.4794	$137.48	$137.50	$137.50
Purchase #2	$118.50	12.676%	$133.5211	$133.52	$133.50	$133.50
Purchase #3	$94.88	8.112%	$102.5767	$102.58	$102.60	$102.60
Purchase #4	$49.67	4.497%	$51.9037	$51.90	$51.90	$51.90
Purchase #5	$32.46	9.166%	$35.4353	$35.44	$35.45	$35.40
Purchase #6	$51.38	5.501%	$54.2064	$54.21	$54.20	$54.20
Purchase #7	$230.76	13.740%	$262.4664	$262.47	$262.45	$262.50
7 purchase totals =	$698.46		$777.5890	$777.60	$777.60	$777.60