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	$142.51	8.803%	$155.0552	$155.06	$155.05	$155.10
Purchase #2	$69.78	4.102%	$72.6424	$72.64	$72.65	$72.60
Purchase #3	$102.83	4.196%	$107.1447	$107.14	$107.15	$107.10
Purchase #4	$156.47	11.691%	$174.7629	$174.76	$174.75	$174.80
Purchase #5	$248.72	11.560%	$277.472	$277.47	$277.45	$277.50
Purchase #6	$84.62	8.136%	$91.5047	$91.50	$91.50	$91.50
Purchase #7	$107.34	3.415%	$111.0057	$111.01	$111.00	$111.00
7 purchase totals =	$912.27		$989.5876	$989.58	$989.55	$989.60