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	$23.27	6.723%	$24.8344	$24.83	$24.85	$24.80
Purchase #2	$73.44	12.586%	$82.6832	$82.68	$82.70	$82.70
Purchase #3	$153.86	9.125%	$167.8997	$167.90	$167.90	$167.90
Purchase #4	$65.74	10.689%	$72.7669	$72.77	$72.75	$72.80
Purchase #5	$88.82	8.126%	$96.0375	$96.04	$96.05	$96.00
Purchase #6	$154.60	11.158%	$171.8503	$171.85	$171.85	$171.90
Purchase #7	$48.69	6.674%	$51.9396	$51.94	$51.95	$51.90
7 purchase totals =	$608.42		$668.0116	$668.01	$668.05	$668.00