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	$132.97	11.574%	$148.3599	$148.36	$148.35	$148.40
Purchase #2	$114.60	11.137%	$127.363	$127.36	$127.35	$127.40
Purchase #3	$46.48	10.654%	$51.432	$51.43	$51.45	$51.40
Purchase #4	$40.35	12.802%	$45.5156	$45.52	$45.50	$45.50
Purchase #5	$21.32	10.345%	$23.5256	$23.53	$23.55	$23.50
Purchase #6	$178.51	11.182%	$198.471	$198.47	$198.45	$198.50
Purchase #7	$228.42	5.609%	$241.2321	$241.23	$241.25	$241.20
7 purchase totals =	$762.65		$835.8992	$835.90	$835.90	$835.90